package main

import "fmt"

type Value float64
type Matrix [][]Value

func Multiply(m1, m2 Matrix) (m3 Matrix, ok bool) {
    rows, cols, extra := len(m1), len(m2[0]), len(m2)
    if len(m1[0]) != extra {
        return nil, false
    }
    m3 = make(Matrix, rows)
    for i := 0; i < rows; i++ {
        m3[i] = make([]Value, cols)
        for j := 0; j < cols; j++ {
            for k := 0; k < extra; k++ {
                m3[i][j] += m1[i][k] * m2[k][j]
            }
        }
    }
    return m3, true
}

func (m Matrix) String() string {
    rows := len(m)
    cols := len(m[0])
    out := "["
    for r := 0; r < rows; r++ {
        if r > 0 {
            out += ",\n "
        }
        out += "[ "
        for c := 0; c < cols; c++ {
            if c > 0 {
                out += ", "
            }
            out += fmt.Sprintf("%7.3f", m[r][c])
        }
        out += " ]"
    }
    out += "]"
    return out
}

func main() {
    A := Matrix{[]Value{1, 2, 3, 4},
        []Value{5, 6, 7, 8}}
    B := Matrix{[]Value{1, 2, 3},
        []Value{4, 5, 6},
        []Value{7, 8, 9},
        []Value{10, 11, 12}}
    P, ok := Multiply(A, B)
    if !ok {
        panic("Invalid dimensions")
    }
    fmt.Printf("Matrix A:\n%s\n\n", A)
    fmt.Printf("Matrix B:\n%s\n\n", B)
    fmt.Printf("Product of A and B:\n%s\n\n", P)
}