gonum.org/v1/gonum v0.17.0: mat.NewDense

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify mat.NewDense in pkg:golang/gonum.org/v1/gonum@v0.17.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/gonum.org/v1/gonum@v0.17.0
Demonstrate these symbols/APIs:
  - mat.NewDense

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:7cfeb31f35d3368d973aec41fb49c7302ce5eb5f3834e779d9715a4b11fd1b56","contract":["mat.NewDense creates a matrix with specified dimensions and populates elements from row-major data slice","mat.NewDense allocates a zero-initialized matrix when data slice is nil","mat.NewDense shares underlying storage with the provided data slice","mat.NewDense panics when length of data slice does not equal rows times columns","mat.NewDense panics when rows or columns dimension is negative"],"goal":"verify mat.NewDense in pkg:golang/gonum.org/v1/gonum@v0.17.0","kind":"HOW","packages":["pkg:golang/gonum.org/v1/gonum@v0.17.0"],"schemaVersion":1,"symbols":["mat.NewDense"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/gonum.org/v1/gonum@v0.17.0"],"schemaVersion":1,"subject":"pkg:golang/gonum.org/v1/gonum@v0.17.0","symbols":["mat.NewDense"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require gonum.org/v1/gonum v0.17.0

gonum.org/v1/gonum v0.17.0 h1:VbpOemQlsSMrYmn7T2OUvQ4dqxQXU+ouZFQsZOx50z4=
gonum.org/v1/gonum v0.17.0/go.mod h1:El3tOrEuMpv2UdMrbNlKEh9vd86bmQ6vqIcDwxEOc1E=

package main

import (
	"fmt"

	"gonum.org/v1/gonum/mat"
)

func main() {
	// Create a 2x3 matrix from a row-major slice of float64
	data := []float64{
		1.0, 2.0, 3.0,
		4.0, 5.0, 6.0,
	}
	m := mat.NewDense(2, 3, data)

	r, c := m.Dims()
	fmt.Printf("Matrix dimensions: %d rows x %d cols\n", r, c)
	fmt.Printf("Element at (0, 1): %.1f\n", m.At(0, 1))

	// Create an uninitialized 2x2 matrix (all zeros)
	emptyMat := mat.NewDense(2, 2, nil)
	emptyMat.Set(0, 0, 42.0)
	fmt.Printf("Zero-allocated matrix element at (0, 0): %.1f\n", emptyMat.At(0, 0))
}

{
  "schemaVersion": 1,
  "goal": "verify mat.NewDense in pkg:golang/gonum.org/v1/gonum@v0.17.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/gonum.org/v1/gonum@v0.17.0"
  ],
  "symbols": [
    "mat.NewDense"
  ]
}

package main

import (
	"fmt"
	"math"
	"os"

	"gonum.org/v1/gonum/mat"
)

func main() {
	// Assertion 1: mat.NewDense creates a matrix with specified dimensions and populates elements from row-major data slice
	data := []float64{
		1.0, 2.0, 3.0,
		4.0, 5.0, 6.0,
	}
	m := mat.NewDense(2, 3, data)
	r, c := m.Dims()
	if r != 2 || c != 3 {
		fmt.Fprintf(os.Stderr, "FAIL: unexpected dims: got (%d, %d), want (2, 3)\n", r, c)
		os.Exit(1)
	}
	if math.Abs(m.At(0, 0)-1.0) > 1e-9 || math.Abs(m.At(0, 1)-2.0) > 1e-9 || math.Abs(m.At(0, 2)-3.0) > 1e-9 ||
		math.Abs(m.At(1, 0)-4.0) > 1e-9 || math.Abs(m.At(1, 1)-5.0) > 1e-9 || math.Abs(m.At(1, 2)-6.0) > 1e-9 {
		fmt.Fprintf(os.Stderr, "FAIL: matrix elements do not match row-major slice\n")
		os.Exit(1)
	}

	// Assertion 2: mat.NewDense allocates a zero-initialized matrix when data slice is nil
	zeroMat := mat.NewDense(3, 2, nil)
	zr, zc := zeroMat.Dims()
	if zr != 3 || zc != 2 {
		fmt.Fprintf(os.Stderr, "FAIL: zero-allocated matrix dims mismatch: got (%d, %d), want (3, 2)\n", zr, zc)
		os.Exit(1)
	}
	for i := 0; i < 3; i++ {
		for j := 0; j < 2; j++ {
			if zeroMat.At(i, j) != 0.0 {
				fmt.Fprintf(os.Stderr, "FAIL: zeroMat at (%d, %d) is non-zero: %f\n", i, j, zeroMat.At(i, j))
				os.Exit(1)
			}
		}
	}

	// Assertion 3: mat.NewDense shares underlying storage with the provided data slice
	backing := []float64{10.0, 20.0, 30.0, 40.0}
	sharedMat := mat.NewDense(2, 2, backing)
	backing[0] = 99.0
	if math.Abs(sharedMat.At(0, 0)-99.0) > 1e-9 {
		fmt.Fprintf(os.Stderr, "FAIL: mutating backing slice did not reflect in matrix element: got %f, want 99.0\n", sharedMat.At(0, 0))
		os.Exit(1)
	}
	sharedMat.Set(1, 1, 88.0)
	if math.Abs(backing[3]-88.0) > 1e-9 {
		fmt.Fprintf(os.Stderr, "FAIL: mutating matrix did not reflect in backing slice: got %f, want 88.0\n", backing[3])
		os.Exit(1)
	}

	// Assertion 4: mat.NewDense panics when length of data slice does not equal rows times columns
	shapePanicked := false
	func() {
		defer func() {
			if r := recover(); r != nil {
				shapePanicked = true
			}
		}()
		_ = mat.NewDense(2, 2, []float64{1.0, 2.0, 3.0})
	}()
	if !shapePanicked {
		fmt.Fprintf(os.Stderr, "FAIL: mat.NewDense did not panic on mismatched slice length\n")
		os.Exit(1)
	}

	// Assertion 5: mat.NewDense panics when rows or columns dimension is negative
	negPanicked := false
	func() {
		defer func() {
			if r := recover(); r != nil {
				negPanicked = true
			}
		}()
		_ = mat.NewDense(-1, 2, nil)
	}()
	if !negPanicked {
		fmt.Fprintf(os.Stderr, "FAIL: mat.NewDense did not panic on negative row dimension\n")
		os.Exit(1)
	}

	fmt.Println("All gonum mat.NewDense contract assertions passed.")
}