1 files changed, 34 insertions, 0 deletions
diff --git a/coding-exercises/2/37.rkt b/coding-exercises/2/37.rkt
new file mode 100644
index 0000000..4acdc18
--- /dev/null
+++ b/coding-exercises/2/37.rkt
@@ -0,0 +1,34 @@
+#lang racket
+(require "../../shared/lists.rkt")
+
+(define (dot-product v w)
+  (accumulate + 0 (map * v w)))
+
+(define (matrix-*-vector m v)
+  (map (lambda (m-row)
+         (accumulate + 0 (map * m-row v))) m))
+
+(define (transpose mat)
+  (accumulate-n cons '() mat))
+
+(define (matrix-*-matrix m n)
+  (let ((cols (transpose n)))
+    (map (lambda (m-row)
+           (map (lambda (n-col)
+                  (dot-product m-row n-col)) cols)) m)))
+
+(define test-m (list (list 1 2 3 4)
+                     (list 4 5 6 6)
+                     (list 6 7 8 9)))
+(define test-n (list (list 1 2 3)
+                     (list 4 5 6)
+                     (list 6 7 8)
+                     (list 6 7 8)))
+(define test-v (list 1 2 3 4))
+((lambda ()
+   (newline)
+   (display (matrix-*-vector test-m test-v))
+   (newline)
+   (display (transpose test-m))
+   (newline)
+   (display (matrix-*-matrix test-m test-n))))