Against Object Pools

Do not use object pools in your library

Instead expose an interface for applications to implement their own object pools, such as:

interface Lender<T>
{
    T borrow();
    return(T obj);
}

Why? By definition, an object pool is a leaky abstraction. Quite literally, an object pool holds onto memory once it has allocated it (usually). This means users of your library will need to know about your library's object pools when chasing down a memory leak. However, that is not to say that object pools are bad, they can play a crucial role in reducing allocation times, and help with garbage collection overhead. But whether this optimization is worth the trade-off can only be known at the application level.

Open Source 2025 Notes

Throwback Thursday: Old School Optimization Using Newfangled Machine Learning

Linear Programming

• "Programming" in the sense of scheduling.
• Inequalities carve out regions of space. These are called "constraints".
• Objective function: goal we are trying to maximize.

Linear Optimization Facts

• Solvable when bounded.
• Min-Max duality.
  • As an example - RPGs: Max strength == min weakness
• Deterministic - guarantees best answer given the input. Is susceptible to garbage input.

When to use

• Making the best choice out of many available while satisfying constraints.
  • Resource allocation.
  • Matching.
  • Routing problems.
  • Inventory decisions.
• Best fit for batch decisions under constraints.

Expected Outcomes

• Better use of resources.
• Stable operations planning.
  • Better inventory management

Pros of Linear Programming

• Measured risk, explainable, and respects your contraints. Can be built quickly with a small team.
• Plays nice with forecasted values: making best prediction with the data available.
• Any vertex of the feasible region has a cone of normal vectors where it is the optimal solution.
• Strength of forecast affects the feasible region.

How to Make One?

• Pyomo functions like an ORM for interfacing with solvers.
• CBC (COIN-OR Branch Cut) to solve.

React at Work Post-Create-React-App

• Provided testing, bundling, and a dev server built-in.
• "Kill it with Fire" book looks interesting.
• Create React App officially deprecated in February 2025.
  • React 19 doesn't work well with it.
  • React is slowly becoming its own framework instead of just acting as a component in a bring-your-own-framework model.

Alternatives

Next.js

Cons:

• Tight coupling of backend and frontend.
• Built-in server runtime.

Remix

• Also tightly coupled.
• Gnarly nested routing structure.

Bun

• Really fast bundler.
• Too much magic.
• Incomplete ecosystem compatibility.

Vite

• Fast, flexible, and friendly.
• Pretty easy to migrate from CRA.
• Static by default.
• Unbundled dev server, optimized builds.
• Can use existing rollup plugings.

Open Source Tooling and Best Practices to Improve Vulnerability Management

• VM: Vulnerability Management

• --Identification -> Reporting -> Evaluation -> Prioritization -> Remediation -- ∧ | | ∨

• Competency trap: people don't use new tools because building competency in a new tool is challenging.
• Mend Renovate: formerly Renovate.
• Renovate bot can work off of dependencies defined in comments in a dockerfile.

Beyond the Chatbot: Delivering Business Value with LLMs

• According to IBM "Institute of Business Value", only 25% of AI initiatives have delivered expected ROI.
  • 16% have scaled enterprise wide.
  • IBM's Advice: ignore FOMO, lean into ROI.
• When to chatbot:
  • Onboarding users (employees/customer) to complex systems.
  • When users are lost, confused, or not even sure what they need.
• Need metrics
  • conversion rate
  • % requests routed to a human
  • manual time saved
  • response/execution times.
• When not to chatbot:
  • Simple forms
  • When users are experts
  • LLM Assisted Automation (agents) can provide value by performing tasks on triggers.
  • Using AI to capture business that you don't have the number of people to take in the business?!?!
• Solving problems with GenAI:
  • Classifying unstructured data.
    • What kind of document is it? What needs to be done with it?
  • Convert unstructured so structured data?
    • Parsing quote requests, emails, etc.
  • Translate similar data between systems:
    • Referencing information from external vendor systems.
• Why was something not already automated?
  • Complex SOPs (Standard Operating Procedures).
  • Unstructured data
  • Parsing information from multiple internal/external services

Measuring GenAI Solutions

LLM Evals

"Answer true or false" is the key.

• Example:

SYSTEM: Act as a metallurgy expert. Do not explain your answer. Answer true or false.

USER: Steel is an alloy of iron and carbon?

Easy to apply to any business domain. Ask experts: what are the toughest questions you're asked? What are the perfect 20 year veteran answers? Then let the expert decide when the AI is trustworthy enough.

Metrics Driven Development

• Answer correctness
  • True/false, multiple choice questions
  • More complex questions:
    • Determine ground truth
    • Take intersection of model answers and ground truth and divide by intersection + model + ground truth.
      • AnswerIntersections / (AnswerIntersections + Ground Truth + Model Answers)
• Faithfulness - degree to which outputs align with facts
• Relevancy
• Context recall
• Arize Phoenix: LLM evaluation tool
• guardrailsai.com

These tools are generally used to test existing LLM's, not to fine tune or create a new model. Most things that are changed by the LLM implementer are the context that is fed in, or the prompt that is given.

Minnesota Code Freeze Conference Notes

My notes from the 2025 Minnesota Code Freeze conference that took place at the University of Minnesota.

Working Effectively with Legacy Code

Michael Feathers (r7k)

• Test-Driven Architecture (like TDD but for architecture).
• Hyrum's Law: Any behavior you expose on an API will become depended upon even if it's not intended.
• Knowledge tends to dissipate over time (think music popularity reduction over time, for example, the ragtime of the 1920's).
• Galileo's scaling law (the square/cube law) - structure must change as things grow:
  • Initially named after the concept that as an object grows its volume grows faster than the surface (n^3 > n^2).
  • However, applies to other scaling concerns, for example, you can't build a skyscraper with wood.
  • With graphs, as they grow, you need to break them into smaller graphs to manage them effectively.
  • Understanding this tension can improve design.
• Miller's law - humans can track 7 +/- 2 items
  • This relates to class design, a class with 20 methods is much harder to track than a class with around 7.
• "The Principle of Deliberate Context" (coined by Michael Feathers):
  • Systems should be designed with intentionally bounded contexts that are optimally sized for human cognition.
• Robustness principle: be liberal in what you accept and conservative in what you produce.
• A potential issue with AI is when it generates things that we don't understand.

Infrastructure as Code Anti-Patterns

Jason Baker (Director of Cloud Operations at Civix)

• Thought on anti-patterns: every anti-pattern started as a pattern with good intentions.
• Why do infrastructure as code anti-patterns exist?
  • Senior tech leadership usually is promoted through software not infrastructure (citation needed).
  • Defining infrastructure as code is immature compared to software development (isn't infrastructure as code software development?).

1. Cloud Cowboys

• Creating cloud infrastructure manually (using a web console) instead of using code.

1. Muti-Tool Madness

• Using too many tools to define the infrastructure.
• Increased complexity, risk, and toil.
• Picking a consistent tool is more important than pick the best tool.

1. Partitioning infrastructure projects by infrastructure type or environment instead of by context.
2. Building all the environments

• Using a single infrastructure template to build out all environments.
• Templates should be environmentally agnostic.
• Infrastructure changes should be promoted using the same process as normal software.

1. One repo to rule them all

• Defining all resources using infrastructure code in one monolithic infrastructure code repository.
• Can introduce undesirable coupling.
• Partition infrastructure code by services.

1. Using DRY With Infrastructure

• All software problems can be solved with another layer abstraction, except for the problem of too many layers of abstraction.
• Taking an imperative approach to building infrastructure instead of a declarative approach.
• Coupling vs. cohesion

1. Modularize all the things

• Same as above.
• Enforce the updating of module versions across projects, allowing no more than for example 2 versions in use.

1. The infra team

• All infrastructure code has to be defined by an infrastructure team.
• Reinforcese the traditional division between developer and infrastructure operations.
• A single team becomes a major bottleneck for infrastructure work.
• In high-performing organizations most of the infrastructure code is defined by software developers and co-located in application repositories.

1. All security related infrastructure code changes must be implemented and approved by the secuirty team.

Finite State Machines and AI

Adam Terlson (https://github.com/adamterlson/AgenticStateMachines)

• Using state machines to control AI agents.
• X State: state management and orchestration library
• Model-based testing of state machines
• His AI Agent definition:
  • Autonomous - operates independently, making decisions without constant human input
  • Goal-oriented - achieves specific objectives
  • Context-aware
  • Collaborates
  • Interactive
  • Persistence - retains memory of past interactions and data.
  • Adaptive
• Agentic Systems:
  • Actors provide autonomy and communication.
  • State machines provide structure, enforce predictable behavior.
  • AI provides adaptability.
• Patterns:
  • Tool use
    • Available tools given to LLM.
    • LLM returns JSON object describing a method (tool) call.
    • Expected next message is tool response.
  • Human in the Loop (tool approval, if tool is expensive).
  • Feedback: one oagent receives the output of another agent and gives feedback on how to improve.
  • Collaboration: multiple specialist agents working on a broader goal where each agent owns a slice of the broader task.
  • Orchestration: Planning agent dynamically routes to the next agent based on current context.
  • "Chartering": state machine defined by LLM.
• Advantages over industry tools?
  • (LangGraph and competitors)

Evolveable Architectures

Rebecca Parsons

• Conway's law - the systems you build will reflect the dysfunction of your organization.
• Last responsible moment - wait to make decisions until the last possible moment.
• How do we build code that is auditable?
• How do we build code that increases code quality?
• Contract testing allows developers to ignore each other.
• Use AI for contract testing?
• LLM hallucinations are a feature, not a bug. How are you supposed to generate something new if you never make something up? The question is whether there are ways to bound the hallucinations (yes, with temperature).
• How do you test non-deterministic systems?

Monolith vs. Platform vs. Serverless

Corwin Diamond

• This talk was generally biased against monoliths (seemed to imply a definition of a monolith as a giant legacy application, in something like an older ecommerce server application).
• CAP Theorem:
  • Consistency - works correctly.
  • Availability - always works.
  • Partition Tolerance - works across different partitions.
  • You can pick 2.
• Distributed CAP: different services/teams within your ecosystem will have different CAP requirements.
• Multi-cluster platforms...
  • Need to solve data replication.
  • Sounds like classic SOA/microservice problems.
• Cellular architecture...
  • Platform monoliths.
• Modularize abstract abstractions.
• Minimize different types of deployment processes.
• Remove requireemnts that aren't required.

Panel

David Laribee, Rebecca Parsons, Michael Feathers

• Remote work:
  • How can we maximize the effectiveness of in-person time?
  • Shoud do hybrid meetings remote first.
  • Important to work on things together with remote work.
  • Create venues where smaller collaborations can occur.
  • Times when we get together should be treated as precious and valuable.
  • Is the problem encouraging people to value social connections?
• Modular Monoliths:
  • Return to simplicity.
  • Look into testcontainers.
  • It is important at the early stages of a product development to develop a well-structured monolith.
  • Chris Richardson has good ideas on microservices.
  • Event-driven applications can be done in process (and I do).
• Functional programming:
  • "The little lisper", "the little schemer" books.
  • If one spends too much time in the OOP world, it can become difficult to understand functional programming.
  • More people are recognizing the benefits of functional programming.
• How do we discern when we should adhere to new programming principles vs traditional principles?
  • With low-code/no-code, you can get started very easily, but it's hard to scale to complex problems.
    • It's easy to solve 80% of the problem, hard to solve the remaining 20%.
  • Be very cautious about de-scaling your development.
  • Where have all the mid-level engineers gone :D.
• Is agile dead?
  • Agility was kind of jettisoned, and "agile" became a management practice.
  • Good technology (and good process?) disappear, they just become standard operating procedure, like small commits, TDD, etc.
  • There are different product domains: Simple, Complex, and Chaotic. Which domain your product fits in determines how "agile" you need to be.
• 3 things developers can do to stay current:
  • Need to start using AI.
    • How are they going to make money off of it?
  • Everyone is using AI today which differs from the prior AI hype cycles of the 60's and 80's.
    • And problematically, most people do not have a strong mental computational model that matches how it really works.
  • AI is good at ideation. It can also help increase your skill at asking questions.

June 17th, 2024

Targeting Multiple Form Factors on Android

If you'd want to target multiple form factors on Android for a single application, you suffer from a case of too many options:

• Provide the same app:
  • Views that adapt to different view dimensions.
  • Views that render differently depending on flags given during the launch of the application (typically via intent).
• Provide different apps:
  • Different product flavors or different modules:
    • Different application IDs.
    • Different version codes.

This means there are 6 (2 + 2*2) possible ways of providing a different application based on the deployed form factor. So how to choose the best?

First off, the "different apps design" seems mostly intended for completely different applications that share the same codebase; the fact that you can use it for different form factors seems to just be a nice side effect. This means that this approach really works best with different applications - with different application IDs, you don't need to worry about collisions when providing application artifacts on Google Play. The downside is that this leaves you with two separate apps as far as Google Play is concerned, or two different version code tracks. If you take the "different version code" and later consolidate your handheld and TV apps, with the TV app being on the "higher" version code track, users will have to for example uninstall the existing TV application. One thing to be aware of with this approach is that once set-up in the Google Play store, it is difficult to reverse.

The other approach is to modify your views given different view dimensions or different Intent information. For TV, for example, this can be discerned by launching a special activity that is filtered on the android.intent.category.LEANBACK_LAUNCHER intent category. While having a single app makes publishing to the app store easier, it does leave both your TV users and your handheld users with the whole app, even though they may not use large swaths of it. Sharing views between TV and handheld is harder than it seems, at least with Jetpack compose, as the API's between touch and D-Pad navigation are largely separate.

Regardless of approach, it feels like swimming upstream trying to have the same app in different form factors. The ideal would to be able to produce different applications per form-factor that can share application ID and version code. Absent that, I think the best approach is unfortunately to maintain a single application.

April 9th, 2024

Rust seems like the perfect language for an LLM-driven programming agent, because the compiler has so many safeguards, that often the best way to build the best program is often to just iterate until your program passes the compilers tests anyways.

March 23rd, 2024

Bittorrent is Dying, NFT's were dumb, but together they could be great?

This is probably an already explored idea, but I quite like the idea for digital art of some sort of proof-of-sale/proof-of-ownership system that uses a git-like (or blockchain-like) structure, which contains magnet links for that digital art, with the digital art itself remaining unencrypted. I think something like this would give society a neat way to appreciate artists for their work without having to lock down said work. Maybe this is what NFT's already are, I don't know!

March 18th, 2024

A defining feature of an asynchronous operation is that it is cancellable.

March 5th, 2024

Good programing is more about good judgment than anything else.

The Interaction State Primitive

I've been developing UI's in some form or another for about 25 years. It's taken nearly that long to realize the basic primitive of dynamic UI's: what I call the "Interaction State" primitive. The Interaction State primitive has these rules:

1. The current state of the property can be accessed via a normal get accessor. In Java, this might be a method with a signature like T getValue(). Sometimes this is called a snapshot, but I prefer the more direct terminology of state. In a language with more syntactical magic available, it can be done via something like a get accessor.
2. Its value can be updated via a normal set accessor. In Java, this might look like setValue(T value). Again, in other languages, syntax magic can make the write access more terse.
3. Updates to the property's state are observable. Below, I will cheat and use the ReactiveX flavors to achieve this.
4. setValue(T value) only notifies observers the value is updated when the new value is not equal to the existing value. This should follow normal equality rules of the language.

I am not the first to make this observation; KnockoutJS, which I used c.a. 2014, had observables in Javascript, and Rx.Net and other ReactiveX flavors have been around for quite some time, with the BehaviorSubject<T>, which has the above semantics, but with slightly contorted syntax. However, in my opinion, all of these languages and libraries don't make it plain that these are the rules they're following. Perhaps the authors of these API's think these rules are obvious and don't need to be broadcast. However, these rules weren't made plain to me until I came across the StateFlow type in Kotlin: upon observing it's simplicity, the lack of too much magic or layers of obfuscation, this raw form of the Interaction State primitive made it all obvious to me.

What benefits does this Interaction State primitive give?

• When used as the main representation of the data state in a View Model, they're easily testable; the current state of the property can be taken just by calling getValue(), and if you want to validate how the property changes over time, you can easily do that too.
• When the observable portion is implemented using something like the Reactive extensions, you can observe its value over time with endless numbers of operators. Using something very generic like Reactive extensions instead of something like StateFlow leaves you very free of any assumptions made about the runtime or environment; for example, you don't have to mess with coroutine contexts or anything like that.
• Integrates very nicely with dynamic UI frameworks; React obviously has its state variables, Jetpack Compose has the magical stateOf and mutableStateOf, and C# has the INotifyPropertyChanged magical interface, and the Interaction State primitive can integrate very nicely with all of them! It also integrates well with something like WinForms.

I want to show some examples of how this primitive can be used in different languages, with a fairly simple use case: given expenses and incomes, display the networth.

Kotlin and Jetpack Compose

Here's an example in Kotlin, integrating with Jetpack Compose:

// The read-only interface for the Interaction State Primitive
abstract class InteractionState<T> : Observable<NullBox<T>>() {
    abstract val value: T
}

// A mutable implementation of the read-only interface for the Interaction State Primitive.
class MutableInteractionState<T>(private val initialValue: T) : InteractionState<T>() {

    // RxJava has the unfortunate design decision of nulls not being allowed as values, so we 
    // box the value to allow nulls.
    private val behaviorSubject = BehaviorSubject.createDefault(NullBox(initialValue))

    override var value: T
        get() = behaviorSubject.value?.value ?: initialValue
        set(value) {
            if (behaviorSubject.value != value)
                behaviorSubject.onNext(NullBox(value))
        }

    override fun subscribeActual(observer: Observer<in NullBox<T>>?) {
        behaviorSubject.safeSubscribe(observer)
    }

    fun asReadOnly(): InteractionState<T> = this
}

class LiftedInteractionState<T: Any>(source: Observable<T>, private val initialValue: T) : InteractionState<T>(), AutoCloseable {

    private val behaviorSubject = BehaviorSubject.createDefault(NullBox(initialValue))
    private val subscription = source.distinctUntilChanged().subscribe { behaviorSubject.onNext(NullBox(it)) }

    override val value: T
        get() = behaviorSubject.value?.value ?: initialValue

    override fun subscribeActual(observer: Observer<in NullBox<T>>?) {
        behaviorSubject.safeSubscribe(observer)
    }

    override fun close() {
        subscription.dispose()
    }
}

class MoneyViewModel(accountManager: ManageAccounts) : ViewModel() {
    val expenses = MutableInteractionState(0.0);

    val income = MutableInteractionState(0.0);

    val networth = LiftedInteractionState(
        Observable.combineLatest(expenses, income).map { expenses, income -> income - expenses },
        0.0);

    suspend fun loadAccount(int accountId) {
        var account = accountManager.loadAccount(accountId);
        expenses.Value = account.Expenses;
        income.Value = account.Income;
    }
}

// easily map MutableInteractionState to mutableStateOf(...)
@Composable
fun <T, S : MutableInteractionState<T>> S.subscribeAsMutableState(
    context: CoroutineContext = EmptyCoroutineContext
): MutableState<T> {
    val state = remember { mutableStateOf(value) }
    DisposableEffect(key1 = this) {
        val disposable = subscribe { state.value = it.value }

        onDispose {
            disposable.dispose()
        }
    }

    LaunchedEffect(key1 = this) {
        value = state.value
        if (context == EmptyCoroutineContext) {
            snapshotFlow { state.value }.collect {
                value = it
            }
        } else withContext(context) {
            snapshotFlow { state.value }.collect {
                value = it
            }
        }
    }
    return state
}

// The Compose view
fun MoneyView(viewModel: MoneyViewModel) {
    with (viewModel){
        var expensesState by expenses.subscribeAsMutableState()
        StandardTextField(
            placeholder = stringResource("Debit"),
            value = expensesState,
            onValueChange = { expensesState = it }
        )

        var incomeState by income.subscribeAsMutableState()
        StandardTextField(
            placeholder = stringResource("Credit"),
            value = incomeState,
            onValueChange = { incomeState = it }
        )

        val networth by networth.subscribeAsState()
        Text(networth);
    }
}

Typescript and React

Here's my usage in Typescript/React:

// Build up the type definitions
export interface InteractionState<State> extends Subscribable<State> {
    get value(): State;
}

export interface UpdatableInteractionState<State> extends InteractionState<State> {
    set value(state: State);
}


// With Typescript, we have the advantage that we can just inherit from the existing `BehaviorSubject` and here
// make `value()` read-only via interface. Of course it's not enforced in the runtime, but it's good enough for us.
class MutableInteractionState<T> extends BehaviorSubject<T> implements UpdatableInteractionState<T> {

    constructor(initialValue: T) {
        super(initialValue);
    }

    set value(value: T) {
        this.next(value);
    }
}

class LiftedInteractionState<T> extends BehaviorSubject<T> implements InteractionState<T> {

    constructor(observable: Observable<T>, initialValue: T) {
        super(initialValue);
        observable.subscribe(this);
    }
}

export function liftInteractionState<T>(observable: Observable<T>, initialValue: T): Observable<T> & InteractionState<T> & SubscriptionLike {
    return new LiftedInteractionState(observable, initialValue);
}

export function mutableInteractionState<T>(initialValue: T): Observable<T> & UpdatableInteractionState<T> & SubscriptionLike {
    return new MutableInteractionState(initialValue);
}

export function useInteractionState<T>(interactionState: InteractionState<T>): T {
    const [state, setState] = React.useState(interactionState.value);

    React.useEffect(() => {
        const sub = interactionState.subscribe({ next: setState });
        return () => sub.unsubscribe();
    }, [interactionState]);

    return state;
}

export function useMutableInteractionState<T>(interactionState: UpdatableInteractionState<T>): [T, Dispatch<SetStateAction<T>>] {
    const state = useInteractionState(interactionState);

    return [
        state,
        (stateOrAction: SetStateAction<T>) => {
            if (stateOrAction instanceof Function) {
                interactionState.value = stateOrAction(interactionState.value);
                return;
            }

            interactionState.value = stateOrAction;
        }];
}

export class MoneyViewModel {
    readonly income = mutableInteractionState(0);
    
    readonly expenses = mutableInteractionState(0);
    
    readonly networth = liftInteractionState(
        combineLatest([this.income, this.expenses]).pipe(map(([i, e]) => i - e)),
        0);
}

const vm = new MoneyViewModel();

export function MoneyView() {
    const income = useInteractionState(vm.income);
    const expenses = useInteractionState(vm.expenses);
    const networth = useInteractionState(vm.networth);

    return <div>
        <input type="text" value={income} onChange={e => vm.income.value = Number.parseFloat(e.target.value)}/>
        <input type="text" value={expenses} onChange={e => vm.expenses.value = Number.parseFloat(e.target.value)}/>
        <div>
            <h3>Networth:</h3>
            <p>{networth}</p>
        </div>
    </div>;
}

C# and WPF

interface IInteractionState<T> : IObservable<T>
{
    public T Value { get; }
}

// Implementing INotifyPropertyChanged as well allows it to be used with WPF/XAML bindings
class MutableInteractionState<T> : IReadOnlyObservableProperty<T>, INotifyPropertyChanged, IDisposable
{

    private readonly BehaviorSubject<T> subject;

    public event PropertyChangedEventHandler PropertyChanged;

    public MutableInteractionState(T initialValue)
    {
        subject = new BehaviorSubject<T>(initialValue);
    }

    public T Value
    {
        get => subject.Value;
        set
        {
            if (!EqualityComparer<T>.Default.Equals(value, subject.Value))
            {
                subject.OnNext(value);
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Value)));
            }
        }
    }

    public IDisposable Subscribe(IObserver<T> observer) => subject.Subscribe(observer);

    public override void Dispose() => subject.Dispose();
}

// A read-only observable
class LiftedInteractionState<T> : IReadOnlyObservableProperty<T>, INotifyPropertyChanged
{
    private readonly BehaviorSubject<T> subject;
    private readonly IDisposable sourceSub;

    public event PropertyChangedEventHandler PropertyChanged;

    public LiftedInteractionState(IObservable<T> source, T initialValue)
    {
        subject = new BehaviorSubject<T>(initialValue);
        sourceSub = source.Subscribe(v => Value = v);
    }

    public T Value
    {
        get => subject.Value;
        private set
        {
            if (!EqualityComparer<T>.Default.Equals(value, subject.Value))
            {
                subject.OnNext(value);
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Value)));
            }
        }
    }

    public IDisposable Subscribe(IObserver<T> observer) => subject.Subscribe(observer);

    public override void Dispose()
    {
        sourceSub.Dispose();
        subject.Dispose();
    }
}

class MoneyViewModel
{
    private readonly IAccountManager accountManager;

    public MutableInteractionState<decimal> Debit { get; } = new(0);

    public MutableInteractionState<decimal> Credit { get; } = new(0);

    public IInteractionState<decimal> Networth;

    public MoneyViewModel(IAccountManager accountManager)
    {
        this.accountManager = accountManager;
        this.Total = new LiftedInteractionState<decimal>(
            this.Credit.CombineLatest(this.Debit).Select(tuple =>
            {
                var (credit, debit) = tuple;
                return credit - debit;
            }),
            0);
    }

    public async Task LoadAccount(int accountId) {
        var account = await accountManager.LoadAccount(accountId);
        Debit.Value = account.Debit;
        Credit.Value = account.Credit;
    }
}

<Window>
    <Grid>
        <TextField Value={Binding Debit.Value} />
        <TextField Value={Binding Credit.Value} />
        <TextLabel Value={Binding Networth.Value} />
    </Grid>
</Window>

In my opinion, removing the obscurity around this primitive has a similar effect to understanding the Promise; it opens up and simplifies a whole class of programming problems: with the Promise, a single definition is wrapped around building asynchronous functions and receiving their results, likewise, for the "Interaction State" primitive, a single definition is given to making a UI that reacts to inputs agnostic of the source; in other words, regardless of whether the UI needs to respond to user input or the UI needs to respond to asynchronous calls, the situation will be handled in the same way by the "Interaction State" primitive. It also enables a programmer to use it for purposes beyond what the implementations above restrict the user to; for example, I've used the Kotlin implementation in both Android XML views and Jetpack Compose, likewise, I've used the C# implementation for common code between WinForms views and WPF views. This allows my view models to remain stable, while only the decoration is updated with new binding syntax.

November 29th, 2023

A core component of learning is separating signal from noise on a given subject. The corollary is that a core component of teaching a subject is informing the student which parts are noise; the signal falls out from this.

November 1st, 2023

Having dealt with C# DLL hell for years, and then going through the equally hellish dotnet HttpClient fiascos, and now struggling with adopting ES modules in a Typescript library, I am beginning to believe that Microsoft has a department focused on making module resolution a living hell for anyone who uses their tools.

Solid Freeform 2023 Notes

From August 14-16, 2023 I attended an academic conference on 3D printing research, below are my notes.

Technion Additive Manufacturing Center

• Current geometric design pardigm ha sbeen with us for over a decade
• V-rep operations:
  • Filleting and rouding
  • Mixed symbolic/numeric computations over multivariate (and V-rep) splines
• https://csaws.cs.technion.ac.il/~gershon/irit

In-Situ Process Monitoring in AM

Michael J. Heiden

Purpose, Motivation

• Failure mode analysis (ie spike in oxygen)
• Reduce coupon inspection
• Runs in parallel with the build process

Detection Methods and Processes

• Optical IR
• Use the Peregrine machine learning model from Oakridge
• Use multi-modal data (thermal imaging/thermography, high speed cameras, spectroscopy, acoustic monitoring)

Using the Data to Create Useful 3D Digital Twins

• Show discrepancies between what is supposed to be printed and the actual

Future Targets

• Real time monitoring
• Closed lop control for defect correction (this is what we do!)

Machine Learning Applied to Process Monitoring for Laser Hot Wire Directed Energy Deposition

Carnegie Mellon University

Comparison with Laser Powder Bed Fusion

• Under acceptable conditions, melt pools are not stable
• Monitoring of rare unwanted events such as spatter requires significant ML traning (1k-10k hand-labeled images)

Laser Hot Wire Additive Manufacturing

• Well behaved melt pools under normal conditions
• Can monitor entire buildds in real time
• Approach: detect unsteady behavior of the melt pool, don't attempt to learn the appearnce of irregular events

Methodology

• Many flaws exist across multiple frames, so a time dependent analysis is beneficial
• Long Short-Term Memory networks are able to learn time dependencies in video data
• Use previous frames to predict future frames (about 10-20 frames of past history)
• Capture a regularity scorePredicition: within 5-10 years we will see fully sensed and automated DED systems

Known Flaw Types

• Stable Deposition
• Melt pool oscillation
• Arcing
• Wire stubbing
• Wire dripping

Summary and Conclusions

• ML model detects unsteady behavior, which is indicative of process instability (unlike LBPF)
• Prediction is that DED systems will be deployed with fully automatic quality control in next 5-10 years

Area Printing

• Area printing is stamping on the powderbed
• Seurat is the company that developed this technology

Rethinking Additive Manufacturing

• DfAM transcends disciplinary boundaries
• Traditional manufacturing informs our design sensibilities
• Evaluate design using consensual design techniques
• DfAM increases as experience increases
• Restrictive DfAM: "Can we print it"
• Opportunistic DfAM: "Should we print it"
• Unlearning requires designers to identify good DfAM solutions
• VR can help with DfAM
• Use VR for simulating a printer in test?
  • Probably not super beneficial for our needs

Co-deisgn of 3D Printing

• You cannot monitor your way out of trouble: need all the insights possible from in-situ and operando monitoring.
• In aircraft manufacturing: "Anything that allows you to gain efficiency is worth the manufacturing cost"
• Diffusion Modeling is not sufficient for AM Heat Exchangers
  • Use heat exchangers used with solar energy?
  • Alternate technology: diffusion bonding
• Improved heat exchangers reduces defects?

Physical Validation of Job Placement Optimization in Cooperative 3D Printing

• Traditional vs Cooperative 3D printing
  • Traditional: gantry systems
  • Limited in scalability and flexibility
• Partitioning Strategy: Chunking
  • First chunk into layers (Z-Chunking)
  • XY-Chunking: chunk adjacent chunks at an angle to facilitate bonding of chunks
• Use grid search algorithm (A* Path Planning) to plan robot movement
  • If there are two robots that are going to take a path at the same time, apply a conflict avoidance algorithm
• AMBOTS C3DP
• When a robot moves to a new location, it requires manual calibration

Time Optimal Path Planning for Heterogenous Robots in Swarm Manufacturing

• Continuous spatial profile with arbitrary robot gemoetry that includes orienatation
• Dynamic environment with arbitrary number of obstacles
• Time-optimal solution for multiple agents
• Projecting Dynamic Obstacles
  • Use "safe intervals" to reduce number of computations
  • Based on safe intervals, split the configurations based on what has more than one safe interval
• Limitations:
  • Does not make real-time adjustments
  • Truly centralized optimal planning scales exponentially with the number of agents
• Open questions:
  • How does shape discretizaiton impact solution quality?
  • What is the upper number of agents before it is too computationally expensive?

Layer Wise Prediction of Microstructural Evolution

• Predict grain size and melt-pool depth using thermal model features
• As structure grows, cooling rate decreases
• Prediction using physics-guided machine learning (SVM models)
  • Predict Meltpool Depth
    • Not inuitively explained by process parameters
  • Thermal Feature Correlate to Grain Size
    • Grain size predicted with 90% F-Score
• Cooling rate also decreases with heat build-up

Post Superficial Temperature Monitoring During Additive Manufacturing

• CNN goal is to produce predicted temperature of build
• Best results come from combining a machine learning model, in situ monitoring, and sensors
• Normal Data + Wall Simulation as inputs gives best ML performance on experimental data
• In Situ Sensors + ML models as a "Digital Twin" of how the part will be produced

Optimal Control of Wire DED Systems

• Modeling of a dynamic system usually using ODE
• Optimal Control Theory - https://en.wikipedia.org/wiki/Optimal_control

Framework for Physics Guided Machine Learning

• Process variations are high in AM
• PSP: Process-structure-property

PSP Linkages for In-situ Data

• Predictive Melt-pool Modeling
  • Multi-layer model produced best results
• Predictive Pore-structure Model
• Predictive Surface-height Model

AI Driven In-Situ Monitoring

Intrinsic Keyhole Oscillation

Keyhole: a puncture in the powderbed that leads to an unexpected cavity ("keyhole pore") in the powderbed

• Combine X-Ray imaging and Thermal Imaging
• Intrinsic Keyhole Oscillation
  • Surface tension and coil pressure
  • Liquid flow on the outside of the meltpool increases keyhole size
  • Lower than 30KHz
• Perturbative Keyhole Oscillation
  • Greater than 40KHz

Gradient-weighted Class Activation Mapping (Grad CAM)

• Predict where keyholes will form using an ML model, avoiding further X-Ray synchotron experiments
• An input to the trained model is a simulation of the build

PRISM: Process Parameter Optimization for Selective Manufacturing

• Goldilocks zone:
  • Not enough: lack of fusion
  • Too much: keyhole formulation
• Use machine learning to determine proper process parameters!
• Goal is to achieve high density, assume density is a surrogate for:
  • CTE (Coefficient of thermal expansion)
  • Elastic modulus
  • Strength
  • Toughness
• Data will be published and open source
• ML Driven Design of Experiment
  • Latin hyper cube sample generation
  • Predict Printability using tree algorithm (bounds determined by expert)
  • Predict density using tree algorithms (XGBoost)
• Select candidates: diversity (determined by L2 distance), quality, and random sleection
• Used FLAML to automate experimentation
• Would probably need to re-train per material type

FAIR Knowledge Management System for Additive Manufacturing

• AMMD.nist.gov, AMBench2022.nist.gov
• ASTM F42 - working group developing data models to represent AM

Unconventional Data Sources for Market Intelligence

• Aachen Center for AM
• Market intelligence uses external data over internal data (patent databases, social media, etc.)
• Databases used for research: Amadeus, LinkedIn, Scopus

Digital Twins

• Part qualification is manual and slow
• Can digital twins help understand the process to manufacturing property map?
• Direct Ink Write
• Using robotic automation to generate large amounts of parts and data

Executable for Avant Garde Laser Exposure (EAGLE)

• Common command interfaces
• Ability to support any input file
• Plugin support
• Process Buckets
• Limited interference with machine
• Common Build Data Storage
  • SQL Database on machine or network
• Print Process Flow:
  • Pre-Process
  • Layer Process:
    • Verify -> Scan -> Characterize -> Recoat
  • Post-Process
• EAGLE is written in Rust and Javascript using Tauri
  • Designed to support print files > 100GB

Direction not intention determines destination

In-Situ Monitoring Using Neutron Rays

• Neutrons have high penetration in metals
• Different contrast from X-Rays
• Phase evolution
• In-Situ Laser Metal Deposition
  • Completmentary to lab and synchotron experiments
• In-Beamline Strain Measurement
• Neutrons are non-destructive, tri-axial, and sub-surface
• Additive has a much wider distribution of gamma prime and gamma double prime sizes

X-Ray Compute Tomagrphy

• Determine powder size because that's always going to be stuck on the surface
• Could minimum powder size (and laser amplitude?) define minimum defects size?

SATURN

SCT and MPM Data

• Lack of fusion and keyhole are two major issues (laser power)
• Rnadom forest prediction works with decent acccuracy
• U-net model?
• Some defects will heal automatically, and don't need to be treated
• Non-balanced gain control introduces saturation in the photodiodes
• OEM gives a graphical representation of the data, not a tabular or formatted version
• Photodiodes operate at >11MHz
• Sensor captures images at 400um resolution

Intelligent Process Control

• Using FPGA to provide faster response times
• Goal is to catch a defect within the transient state (10-20us), they've (potentially) achieved nanosecond response times

High precision measurement of Melt Pools

• FPS of 40,000
• Resolution: 896 x 176 pixels

End-to-End AI Models for Error Detection

• Current issue - solutions are not general
• Matta (Cambridge company), Grey-1 AI Copilot for AM
• Multi-head residual attention convolutional neural network:
  • Develops its own masks to determine where to pay attention

Automated Project Publishing

The idea: a small script that periodically runs, checking for changes to project readme's, and publishes updates to davidvedvick.info.

This script would need to reside in a-personal-site. Would need to be configurable so that it could accurately be run on a local machine but also on a build server.

Update 11/28/2023: I instead implemented this as GoCD pipeline that I run on-demand, and it is glorious.