{
 "nbformat": 4,
 "nbformat_minor": 5,
 "metadata": {
  "kernelspec": {
   "display_name": "Python 3",
   "language": "python",
   "name": "python3"
  },
  "language_info": {
   "name": "python",
   "version": "3.11"
  },
  "colab": {
   "name": "week-09-practice.ipynb",
   "provenance": []
  }
 },
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": "# Week 09: Reliability, shift, and error analysis\n\nMachine Learning in Engineering Science | NCKU + LAiMM | Fall 2026\n\n**Purpose:** a fully worked, self-paced in-class practice with an optional extension. Weeks 11 and 18 are optional examination-readiness materials. These notebooks do not create weekly graded assignments.\n\n**Before running:** choose a Python 3 kernel in Jupyter or a CPU runtime in Colab. Run every cell from top to bottom with Shift+Enter. Setup installs missing free packages. No API key or external dataset download is required.\n\n**Learning target:** complete the calculation, inspect intermediate values, and explain why the protocol supports a limited claim.\n\n**Time:** about 25-45 minutes including reading, prediction, execution, and explain-back.\n",
   "id": "cell-000"
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": "## 1. Set up and record the environment\n\nKeep the seed fixed for the first run. Record actual outputs and package versions rather than copying a claimed performance number.\n",
   "id": "cell-001"
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "outputs": [],
   "metadata": {},
   "source": "import sys, subprocess, importlib.util, platform, json, random, hashlib\nfrom pathlib import Path\nrequired = {\"numpy\": \"numpy\", \"matplotlib\": \"matplotlib\", \"sklearn\": \"scikit-learn\"}\nmissing = [package for module, package in required.items() if importlib.util.find_spec(module) is None]\nif missing:\n    subprocess.check_call([sys.executable, \"-m\", \"pip\", \"install\", *missing])\nimport numpy as np\nimport matplotlib.pyplot as plt\nSEED = 2026\nrandom.seed(SEED)\nnp.random.seed(SEED)\nrng = np.random.default_rng(SEED)\nARTIFACTS = Path(\"artifacts\")\nARTIFACTS.mkdir(exist_ok=True)\nprint(\"Python:\", platform.python_version(), \"NumPy:\", np.__version__, \"Seed:\", SEED)\n",
   "id": "cell-002"
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": "**Checkpoint.** The environment cell must finish before any analysis cell. Restart and run all if a variable is missing.\n",
   "id": "cell-003"
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": "## 2. Build a controlled held-out experiment\n\nWe deliberately train and test on a known synthetic relation. Later we change one feature distribution to study sensitivity.\n",
   "id": "cell-004"
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "outputs": [],
   "metadata": {},
   "source": "from sklearn.model_selection import train_test_split\nfrom sklearn.linear_model import Ridge\nfrom sklearn.metrics import mean_absolute_error\nX=rng.normal(size=(500,3)); y=2*X[:,0]+X[:,1]**2+rng.normal(0,.2,500)\nXtr,Xte,ytr,yte=train_test_split(X,y,test_size=.3,random_state=SEED)\nmodel=Ridge().fit(Xtr,ytr)\nresidual=model.predict(Xte)-yte\n",
   "id": "cell-005"
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": "**Checkpoint.** The linear model cannot represent the quadratic term exactly. This is an inspectable model-class limitation.\n",
   "id": "cell-006"
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": "## 3. Inspect subgroup errors\n\nDefine subgroups using a feature range before inspecting outcomes. Error differences can reveal where the model specification fails.\n",
   "id": "cell-007"
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "outputs": [],
   "metadata": {},
   "source": "extreme=np.abs(Xte[:,1])>1\nsummary={\"overall_MAE\":float(np.mean(np.abs(residual))),\n         \"extreme_MAE\":float(np.mean(np.abs(residual[extreme]))),\n         \"ordinary_MAE\":float(np.mean(np.abs(residual[~extreme])))}\nprint(summary)\nplt.scatter(Xte[:,1],residual); plt.axhline(0,color=\"black\")\nplt.xlabel(\"Feature 1\"); plt.ylabel(\"Residual\"); plt.show()\n",
   "id": "cell-008"
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": "**Checkpoint.** Do not report only the overall metric when a subgroup fails systematically.\n",
   "id": "cell-009"
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": "## 4. Stress-test a changed population\n\nGenerate a second population with wider feature 1 values and the same underlying formula. Keep the trained model fixed.\n",
   "id": "cell-010"
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "outputs": [],
   "metadata": {},
   "source": "shifted=rng.normal(size=(150,3)); shifted[:,1]*=2.5\nshifted_y=2*shifted[:,0]+shifted[:,1]**2+rng.normal(0,.2,150)\nsummary[\"shifted_MAE\"]=float(mean_absolute_error(shifted_y,model.predict(shifted)))\nprint(summary)\n",
   "id": "cell-011"
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": "**Checkpoint.** This synthetic stress test isolates one failure mechanism. It does not quantify every real deployment shift.\n",
   "id": "cell-012"
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": "## 6. Preserve your evidence\n\nExport a JSON record with a seed, package version, and measured result. Download the artifacts directory before leaving Colab; runtime storage is temporary.\n",
   "id": "cell-013"
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "outputs": [],
   "metadata": {},
   "source": "record={\"week\":9,\"seed\":SEED,\"numpy\":np.__version__,\"python\":platform.python_version(),\"result\":summary}\n(ARTIFACTS/\"week-09-evidence.json\").write_text(json.dumps(record,indent=2))\nprint(json.dumps(record,indent=2))\n",
   "id": "cell-014"
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": "**Checkpoint.** The evidence file must match the result you actually obtained. A saved screenshot alone does not permit rerunning the calculation.\n",
   "id": "cell-015"
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": "## 7. Try one change and explain it\n1. Predict the effect of one change before editing code. Change one parameter, input, or boundary condition only.\n2. Rerun all cells in a fresh kernel. Keep the original evidence record and compare the observed difference.\n3. Explain the result using the mechanism, not just the final number.\n4. Name one assumption that limits the claim, and a new test that could challenge it.\n\n**Troubleshooting:** if installation fails, restore network access; if a variable is undefined, run earlier cells; if your output differs, compare package versions, seed, and data construction. Do not repeatedly edit code until a preferred score appears.\n\n**Completion criterion:** one executed notebook, one evidence JSON, and a brief claim/evidence/limitation statement.\n\n### Reference documentation\n- [NumPy user guide](https://numpy.org/doc/stable/user/)\n- [scikit-learn user guide](https://scikit-learn.org/stable/user_guide.html)\n- [Course repository](https://github.com/CHjonnyYu/MLES-Fall-2026)\n",
   "id": "cell-016"
  }
 ]
}