gonum.org/v1/gonum v0.17.0: mat.Dense.Mul

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 gonum.org/v1/gonum/mat.Dense.Mul 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:
  - gonum.org/v1/gonum/mat.Dense.Mul

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:sha256:39c03b508ebf2e551b03449102ae098e637232d4cbcbb518e84385ef117b8a77","contract":["mat.Dense.Mul computes the matrix product of two rectangular Dense matrices into an uninitialized receiver","mat.Dense.Mul preserves the identity matrix property where multiplying by identity yields the original matrix","mat.Dense.Mul panics with ErrShape when the inner dimensions of the operand matrices do not match","mat.Dense.Mul panics with ErrShape when the receiver has non-matching dimensions","mat.Dense.Mul supports self-assignment aliasing where the receiver is also an operand"],"goal":"verify gonum.org/v1/gonum/mat.Dense.Mul 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":["gonum.org/v1/gonum/mat.Dense.Mul"]},"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":["gonum.org/v1/gonum/mat.Dense.Mul"],"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() {
	// Define a 2x3 matrix A
	a := mat.NewDense(2, 3, []float64{
		1.0, 2.0, 3.0,
		4.0, 5.0, 6.0,
	})

	// Define a 3x2 matrix B
	b := mat.NewDense(3, 2, []float64{
		7.0, 8.0,
		9.0, 1.0,
		2.0, 3.0,
	})

	// Compute matrix product C = A * B
	var c mat.Dense
	c.Mul(a, b)

	fmt.Printf("Matrix A (2x3):\n%v\n", mat.Formatted(a, mat.Prefix("  ")))
	fmt.Printf("Matrix B (3x2):\n%v\n", mat.Formatted(b, mat.Prefix("  ")))
	fmt.Printf("Product C = A * B (2x2):\n%v\n", mat.Formatted(&c, mat.Prefix("  ")))
}

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

package main

import (
	"errors"
	"fmt"
	"math"
	"os"

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

func equalWithinTol(a, b mat.Matrix, tol float64) bool {
	ar, ac := a.Dims()
	br, bc := b.Dims()
	if ar != br || ac != bc {
		return false
	}
	for i := 0; i < ar; i++ {
		for j := 0; j < ac; j++ {
			if math.Abs(a.At(i, j)-b.At(i, j)) > tol {
				return false
			}
		}
	}
	return true
}

func main() {
	// Assertion 1: mat.Dense.Mul computes the matrix product of two rectangular Dense matrices into an uninitialized receiver
	a := mat.NewDense(2, 3, []float64{
		1, 2, 3,
		4, 5, 6,
	})
	b := mat.NewDense(3, 2, []float64{
		7, 8,
		9, 1,
		2, 3,
	})
	var c mat.Dense
	c.Mul(a, b)

	expectedC := mat.NewDense(2, 2, []float64{
		31, 19,
		85, 55,
	})
	if !equalWithinTol(&c, expectedC, 1e-9) {
		fmt.Fprintf(os.Stderr, "FAIL: rectangular multiplication mismatch\n")
		os.Exit(1)
	}

	// Assertion 2: mat.Dense.Mul preserves the identity matrix property where multiplying by identity yields the original matrix
	m := mat.NewDense(2, 2, []float64{
		2, -1,
		3, 5,
	})
	ident := mat.NewDense(2, 2, []float64{
		1, 0,
		0, 1,
	})
	var cIdent mat.Dense
	cIdent.Mul(m, ident)
	if !equalWithinTol(&cIdent, m, 1e-9) {
		fmt.Fprintf(os.Stderr, "FAIL: identity multiplication mismatch\n")
		os.Exit(1)
	}

	// Assertion 3: mat.Dense.Mul panics with ErrShape when the inner dimensions of the operand matrices do not match
	innerMismatchPanicked := false
	func() {
		defer func() {
			if r := recover(); r != nil {
				if err, ok := r.(error); ok && errors.Is(err, mat.ErrShape) {
					innerMismatchPanicked = true
				}
			}
		}()
		badB := mat.NewDense(2, 2, []float64{1, 2, 3, 4})
		var d mat.Dense
		d.Mul(a, badB) // a is 2x3, badB is 2x2 (3 != 2)
	}()
	if !innerMismatchPanicked {
		fmt.Fprintf(os.Stderr, "FAIL: did not panic with ErrShape on inner dimension mismatch\n")
		os.Exit(1)
	}

	// Assertion 4: mat.Dense.Mul panics with ErrShape when the receiver has non-matching dimensions
	receiverMismatchPanicked := false
	func() {
		defer func() {
			if r := recover(); r != nil {
				if err, ok := r.(error); ok && errors.Is(err, mat.ErrShape) {
					receiverMismatchPanicked = true
				}
			}
		}()
		badC := mat.NewDense(3, 3, nil)
		badC.Mul(a, b) // expected product is 2x2, receiver is fixed at 3x3
	}()
	if !receiverMismatchPanicked {
		fmt.Fprintf(os.Stderr, "FAIL: did not panic with ErrShape on receiver dimension mismatch\n")
		os.Exit(1)
	}

	// Assertion 5: mat.Dense.Mul supports self-assignment aliasing where the receiver is also an operand
	sqA := mat.NewDense(2, 2, []float64{
		1, 2,
		3, 4,
	})
	sqB := mat.NewDense(2, 2, []float64{
		2, 0,
		1, 2,
	})
	sqA.Mul(sqA, sqB)
	expectedAliased := mat.NewDense(2, 2, []float64{
		4, 4,
		10, 8,
	})
	if !equalWithinTol(sqA, expectedAliased, 1e-9) {
		fmt.Fprintf(os.Stderr, "FAIL: aliased self-assignment mismatch\n")
		os.Exit(1)
	}

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