main.go

package main

import (
	"bytes"
	"fmt"
	"strconv"
	"sync"
)

type Matrix struct {
	width  int
	height int
	values [][]float64
}

func Empty(rowHeight int, columnWidth int) Matrix {
	matVals := make([][]float64, rowHeight)
	for row := range matVals {
		matVals[row] = make([]float64, columnWidth)
	}
	return Matrix{rowHeight, columnWidth, matVals}
}

func (m *Matrix) assignValue(row int, column int, val float64) {
	m.values[row][column] = val
}

func Eye(size int) Matrix {
	returnMatrix := Empty(size, size)
	for i := 0; i < size; i++ {
		returnMatrix.assignValue(i, i, 1)
	}
	return returnMatrix
}

func (m Matrix) multiply(n Matrix) Matrix {
	var retMat Matrix
	var wg sync.WaitGroup
	if len(m.values) == len(n.values[0]) { // C1 == R2 {
		retMat = Empty(len(m.values), len(n.values[0]))
	} else {
		return Matrix{}
	}
	for i := range m.values {
		wg.Add(1)
		go func(ig int) {
			defer wg.Done()
			sum := 0.0
			for j := range n.values[0] {
				for k := range m.values[0] {
					sum += m.values[ig][k] * n.values[k][j]
				}
				retMat.values[ig][j] = sum
			}
		}(i)
	}
	wg.Wait()
	return retMat
}

func (m Matrix) String() string {
	var retString bytes.Buffer
	for i := range m.values {
		if i == 0 {
			retString.WriteString("[ ")
		} else {
			retString.WriteString("  ")
		}
		for j := range m.values[i] {
			retString.WriteString(strconv.FormatFloat(m.values[i][j], 'f', 2, 64))
			if j != len(m.values[i])-1 {
				retString.WriteString(", ")
			}
		}
		if i == len(m.values)-1 {
			retString.WriteString(" ]")
		}
		retString.WriteString("\n")
	}
	return retString.String()
}

func main() {
	mat1 := Eye(4)
	mat2 := Eye(4)
	fmt.Printf("%v", mat1.multiply(mat2))
}