Data commit

Task/Cramers-rule/Racket/cramers-rule.rkt

@@ -0,0 +1,28 @@
+#lang racket
+(require math/matrix)
+
+(define sys
+  (matrix [[2 -1 5 1]
+           [3 2 2 -6]
+           [1 3 3 -1]
+           [5 -2 -3 3]]))
+
+(define soln
+  (col-matrix [-3 -32 -47 49]))
+
+(define (matrix-set-column M new-col idx)
+  (matrix-augment (list-set (matrix-cols M) idx new-col)))
+
+(define (cramers-rule M soln)
+  (let ([denom (matrix-determinant M)]
+        [nvars (matrix-num-cols M)])
+    (letrec ([roots (λ (position)
+                      (if (>= position nvars)
+                          '()
+                          (cons (/ (matrix-determinant
+                                    (matrix-set-column M soln position))
+                                   denom)
+                                (roots (add1 position)))))])
+      (map cons '(w x y z) (roots 0)))))
+
+(cramers-rule sys soln)