A-M baby

Task/Matrix-arithmetic/D/matrix-arithmetic.d

@@ -0,0 +1,57 @@
+import std.algorithm, std.range, std.traits, permutations2,
+       permutations_by_swapping1;
+
+auto prod(Range)(/*in*/ Range r) /*pure nothrow*/ {
+    return reduce!q{a * b}(cast(ForeachType!Range)1, r);
+}
+
+T permanent(T)(in T[][] a) /*pure nothrow*/
+in {
+    foreach (const row; a)
+        assert(row.length == a[0].length);
+} body {
+    auto r = iota(cast()a.length);
+    T tot = 0;
+    foreach (sigma; permutations(r.array()))
+        tot += r.map!(i => a[i][sigma[i]])().prod();
+    return tot;
+}
+
+T determinant(T)(in T[][] a) /*pure nothrow*/
+in {
+    foreach (const row; a)
+        assert(row.length == a[0].length);
+} body {
+    immutable n = a.length;
+    auto r = iota(n);
+    T tot = 0;
+    //foreach (sigma, sign; spermutations(n)) {
+    foreach (sigma_sign; spermutations(n)) {
+        const sigma = sigma_sign[0];
+        immutable sign = sigma_sign[1];
+        tot += sign * r.map!(i => a[i][sigma[i]])().prod();
+    }
+    return tot;
+}
+
+void main() {
+    import std.stdio;
+
+    foreach (const a; [[[1, 2],
+                        [3, 4]],
+
+                       [[1, 2, 3, 4],
+                        [4, 5, 6, 7],
+                        [7, 8, 9, 10],
+                        [10, 11, 12, 13]],
+
+                       [[ 0,  1,  2,  3,  4],
+                        [ 5,  6,  7,  8,  9],
+                        [10, 11, 12, 13, 14],
+                        [15, 16, 17, 18, 19],
+                        [20, 21, 22, 23, 24]]]) {
+        writefln("[%([%(%2s, %)],\n %)]]", a);
+        writefln("Permanent: %s, determinant: %s\n",
+                 permanent(a), determinant(a));
+    }
+}