Writing | Christopher Peret

import torch import torch.nn as nn def train(model, loader, epochs=10): opt = torch.optim.AdamW( model.parameters(), lr=3e-4) loss_fn = nn.CrossEntropyLoss() model.train() for epoch in range(epochs): for x, y in loader: x, y = x.cuda(), y.cuda() opt.zero_grad() loss = loss_fn(model(x), y) loss.backward() opt.step() print(f"epoch {epoch} done") class ConvNet(nn.Module): def __init__(self, n_classes=10): super().__init__() self.net = nn.Sequential( nn.Conv2d(3, 32, 3, 1, 1), nn.ReLU(), nn.Conv2d(32, 64, 3, 1, 1), nn.ReLU(), nn.MaxPool2d(2), nn.Dropout(0.25), nn.Flatten(), nn.Linear(64 * 16 * 16, 128), nn.ReLU(), nn.Linear(128, n_classes), ) def forward(self, x): return self.net(x) from torchvision import transforms tfm = transforms.Compose([ transforms.RandomResizedCrop(64), transforms.RandomHorizontalFlip(), transforms.ToTensor(), transforms.Normalize(mean, std), ]) train_ds = ImageFolder("train", tfm) loader = DataLoader( train_ds, batch_size=64, shuffle=True, num_workers=4, ) @torch.no_grad() def evaluate(model, loader): model.eval() correct = total = 0 for x, y in loader: x, y = x.cuda(), y.cuda() pred = model(x).argmax(dim=1) correct += (pred == y).sum() total += y.size(0) acc = correct / total print(f"val acc: {acc:.3%}") return acc model.eval() x = torch.randn(1, 3, 64, 64).cuda() traced = torch.jit.trace(model, x) traced.save("model.pt") # ONNX export for deployment torch.onnx.export( model, x, "model.onnx", input_names=["input"], output_names=["logits"], opset_version=17, ) print("exported model.pt")

import torch import torch.nn as nn def attention(q, k, v, mask=None): d_k = q.size(-1) scores = q @ k.transpose(-2, -1) scores = scores / d_k ** 0.5 if mask is not None: scores = scores.masked_fill( mask == 0, -1e9) w = torch.softmax(scores, dim=-1) return w @ v, w class MultiHeadAttention(nn.Module): def __init__(self, dim, heads=8): super().__init__() self.heads = heads self.qkv = nn.Linear(dim, 3 * dim) self.proj = nn.Linear(dim, dim) def forward(self, x): B, N, D = x.shape h = self.heads qkv = self.qkv(x).reshape( B, N, 3, h, D // h) q, k, v = qkv.unbind(2) out, _ = attention(q, k, v) out = out.reshape(B, N, D) return self.proj(out)

#include <Eigen/Dense> #include <array> #include <cmath> using Vec7 = std::array<double, 7>; using Eigen::Matrix4d; // KUKA iiwa DH parameters constexpr double A[7] = { -M_PI_2, M_PI_2, M_PI_2, -M_PI_2, -M_PI_2, M_PI_2, 0}; constexpr double D[7] = { 0.34, 0.0, 0.40, 0.0, 0.40, 0.0, 0.126}; // One DH link transform Matrix4d link(double a, double d, double q) { double ct = cos(q), st = sin(q); double ca = cos(a), sa = sin(a); Matrix4d T; T << ct, -st*ca, st*sa, 0, st, ct*ca, -ct*sa, 0, 0, sa, ca, d, 0, 0, 0, 1; return T; } // 7-DOF forward kinematics Matrix4d fk(const Vec7& q) { Matrix4d T = Matrix4d::Identity(); for (int i = 0; i < 7; ++i) T *= link(A[i], D[i], q[i]); return T; } using Eigen::Vector3d; using Mat67 = Eigen::Matrix<double, 6, 7>; // Geometric Jacobian at q Mat67 jacobian(const Vec7& q) { Mat67 J; Matrix4d T = Matrix4d::Identity(); Vector3d pe = fk(q).block<3,1>(0,3); for (int i = 0; i < 7; ++i) { Vector3d z = T.block<3,1>(0,2); Vector3d p = T.block<3,1>(0,3); J.block<3,1>(0,i)=z.cross(pe-p); J.block<3,1>(3,i)=z; T *= link(A[i], D[i], q[i]); } return J; } using Eigen::Matrix3d; // Damped least-squares IK step Vec7 ik_step(const Vec7& q, const Vector3d& goal) { auto J = jacobian(q).topRows<3>(); Vector3d e = goal - fk(q).block<3,1>(0,3); double k = 0.05; auto Jt = J.transpose(); Vector3d dx = (J*Jt + k*k*Matrix3d::Identity()) .ldlt().solve(e); Vec7 dq; for (int i = 0; i < 7; ++i) dq[i] = (Jt*dx)(i); return dq; }

use std::collections::BinaryHeap; use std::collections::HashMap; use std::cmp::Ordering; #[derive(Copy, Clone, Eq, PartialEq)] struct Node { cost: u32, pos: (i32, i32), } // min-heap: reverse the ordering impl Ord for Node { fn cmp(&self, other: &Self) -> Ordering { other.cost.cmp(&self.cost) } } impl PartialOrd for Node { fn partial_cmp(&self, other: &Self) -> Option<Ordering> { Some(self.cmp(other)) } } fn heur(a: (i32, i32), b: (i32, i32)) -> u32 { let dx = (a.0 - b.0).abs(); let dy = (a.1 - b.1).abs(); (dx + dy) as u32 } // A* shortest path over a grid fn astar( start: (i32, i32), goal: (i32, i32), adj: impl Fn((i32, i32)) -> Vec<(i32, i32)>, ) -> Option<u32> { let mut open = BinaryHeap::new(); let mut best = HashMap::new(); open.push(Node { cost: 0, pos: start }); best.insert(start, 0u32); while let Some(cur) = open.pop() { if cur.pos == goal { return Some(cur.cost); } for nb in adj(cur.pos) { let g = best[&cur.pos] + 1; let seen = best.get(&nb) .copied() .unwrap_or(u32::MAX); if g < seen { best.insert(nb, g); let f = g + heur(nb, goal); open.push(Node { cost: f, pos: nb, }); } } } None }

writing

Architecture notes and technical explorations

Ideas, experiments, and lessons from building across software and physical systems. Click a post to read it.

July 19, 2026

Building a 100-Player Browser Game for OpenAI Buildweek

Past the midpoint of OpenAI Buildweek. My project holds 100 simultaneous players in one shared world, in the browser, on a C++ authoritative server.

Game DevelopmentNetworkingWeb

July 14, 2026

Two Agents, One Game Engine: Fable 5 vs GPT 5.6 SOL

I ran two frontier coding agents head-to-head on the hardest build I know: a from-scratch 3D multiplayer engine with a strict binary wire budget. One is a senior engineer. One is a principal.

AIAgentsGame DevelopmentNetworking

March 20, 2026

Straight Lines in Latent Space

Temporal straightening for latent planning: regularize the curvature of latent trajectories and gradient-based planning gets dramatically more stable. The leverage is in the representation, not the planner.

AIWorld ModelsRoboticsResearch

September 20, 2025

The npm Supply Chain Is a Standing Risk

Three npm compromises in a matter of weeks: a stolen Nx publish token, the chalk/debug crypto-stealer, and the self-propagating Shai-Hulud worm that reached CrowdStrike's packages. Lock your upgrades.

SecuritySupply ChainJavaScript

September 12, 2025

Posing Robots in the Browser: URDF and MJCF on the Web

AxisLab: view, pose, and physically simulate robot models in the browser. URDF and MJCF, real MuJoCo compiled to WebAssembly. Policy playback was the roadmap. It shipped.

RoboticsSimulationWeb3D

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Architecture notes and technical explorations

Building a 100-Player Browser Game for OpenAI Buildweekopen ↗

Two Agents, One Game Engine: Fable 5 vs GPT 5.6 SOLopen ↗

Straight Lines in Latent Spaceopen ↗

The npm Supply Chain Is a Standing Riskopen ↗

Posing Robots in the Browser: URDF and MJCF on the Webopen ↗

Architecture notes and technical explorations

Building a 100-Player Browser Game for OpenAI Buildweekopen ↗

Two Agents, One Game Engine: Fable 5 vs GPT 5.6 SOLopen ↗

Straight Lines in Latent Spaceopen ↗

The npm Supply Chain Is a Standing Riskopen ↗

Posing Robots in the Browser: URDF and MJCF on the Webopen ↗

Building a 100-Player Browser Game for OpenAI Buildweek

Two Agents, One Game Engine: Fable 5 vs GPT 5.6 SOL

Straight Lines in Latent Space

The npm Supply Chain Is a Standing Risk

Posing Robots in the Browser: URDF and MJCF on the Web

Building a 100-Player Browser Game for OpenAI Buildweek

Two Agents, One Game Engine: Fable 5 vs GPT 5.6 SOL

Straight Lines in Latent Space

The npm Supply Chain Is a Standing Risk

Posing Robots in the Browser: URDF and MJCF on the Web