Add multiplication to Zig Matrix

zig-matrix/src/main.zig

@@ -163,6 +163,37 @@ const Matrix = struct {
         return result;
     }
 
+    pub fn mul(self: Matrix, allocator: std.mem.Allocator, other: Matrix) !Matrix {
+        if (self.cols != other.rows) {
+            return error.IncompatibleDims;
+        }
+
+        var result: Matrix = try Matrix.init(
+            allocator,
+            self.rows,
+            other.cols,
+            &.{},
+        );
+
+        var currRow: u64 = 0;
+        while (currRow < result.rows) : (currRow += 1) {
+            var currCol: u64 = 0;
+            while (currCol < result.cols) : (currCol += 1) {
+                var currSum: i64 = 0;
+                var rowIter = self.row(currRow);
+                var colIter = other.col(currCol);
+
+                while (rowIter.next()) |r| {
+                    currSum += r * (colIter.next() orelse unreachable);
+                }
+
+                try result.set(.{ currRow, currCol }, currSum);
+            }
+        }
+
+        return result;
+    }
+
     pub fn row(self: Matrix, rowIdx: u64) RowIterator {
         return RowIterator.init(
             self,
@@ -343,3 +374,31 @@ test "matrix col iterator" {
     try std.testing.expect(col_iter.next() == 9);
     try std.testing.expect(col_iter.next() == null);
 }
+
+test "matrix mul" {
+    const mat1 = try Matrix.init(
+        std.testing.allocator,
+        2,
+        3,
+        &.{ 1, 2, 3, 4, 5, 6 },
+    );
+    defer mat1.deinit();
+
+    const mat2 = try Matrix.init(
+        std.testing.allocator,
+        3,
+        2,
+        &.{ 1, 2, 3, 4, 5, 6 },
+    );
+    defer mat2.deinit();
+
+    const mat3 = try mat1.mul(std.testing.allocator, mat2);
+    defer mat3.deinit();
+
+    try std.testing.expect(mat3.rows == 2);
+    try std.testing.expect(mat3.cols == 2);
+    try std.testing.expect(try mat3.get(.{ 0, 0 }) == 22);
+    try std.testing.expect(try mat3.get(.{ 0, 1 }) == 28);
+    try std.testing.expect(try mat3.get(.{ 1, 0 }) == 49);
+    try std.testing.expect(try mat3.get(.{ 1, 1 }) == 64);
+}