Add module to generate network nodes and edges.

network.rkt

@@ -0,0 +1,45 @@
+;; Copyright 2019 Edward L. Platt <elplatt@alum.mit.edu>
+;;
+;; TODO: comments and tests
+
+#lang racket
+
+(require "sylvester.rkt")
+
+(define (sylvester-nodes m)
+  (map (compose (extend-sylvester-radix m)
+                make-sylvester-radix)
+       (range (- (sylvester m) 1))))
+
+(define (sylvester-edges m)
+  (foldr
+   append
+   '()
+   (map (lambda (k) (map (sylvester-color-edge k) (sylvester-nodes m)))
+        (range m))))
+
+(define (sylvester-color-edge k)
+  (lambda (v) (list v ((skip-sylvester-radix k) v))))
+
+(define (permutation-sylvester-radix i n)
+  (lambda (v)
+    (let* ([v ((extend-sylvester-radix (+ i 1)) v)]
+           [head (take v i)]
+           [tail (if (< i (- (length v) 1))
+                     (drop v (+ i 1))
+                     '())]
+           [element (list-ref v i)])
+      (append
+       head
+       (cons (modulo (+ element n) (sylvester i))
+             tail)))))
+
+(define (skip-sylvester-radix i)
+  (lambda (v)
+    (if (= i 0)
+        ((permutation-sylvester-radix 0 1) v)
+        (let* ([prev (skip-sylvester-radix (- i 1))]
+               [partial (take v (min i (length v)))]
+               [value (sylvester-radix-value (prev partial))])
+          ((compose (permutation-sylvester-radix i (+ 1 value)) prev) v)))))
+