function multarrays($a, $b) {
    $n,$m,$p = ($a.Count - 1), ($b.Count - 1), ($b[0].Count - 1)
    if ($a[0].Count -ne $b.Count) {throw "Multiplication impossible"}
    $c = @(0)*($a[0].Count)
    foreach ($i in 0..$n) {
        $c[$i] = foreach ($j in 0..$p) {
            $sum = 0
            foreach ($k in 0..$m){$sum += $a[$i][$k]*$b[$k][$j]}
            $sum
        }
    }
    $c
 }

function show($a) { $a | foreach{"$_"}}

$a = @(@(1,2),@(3,4))
$b = @(@(5,6),@(7,8))
$c = @(5,6)
"`$a ="
show $a
""
"`$b ="
show $b
""
"`$c ="
$c
""
"`$a * `$b ="
show (multarrays $a $b)
" "
"`$a * `$c ="
show (multarrays $a $c)