+ variance

lib/fimg-math.c

@@ -68,6 +68,18 @@ for (idx=0; idx<4; idx++) {
 
 return 0;
 }
+/* ---------------------------------------------------------------- */
+/*
+c = 0
+s = x1
+pour j de 2 à n
+  s = s+xj
+  c = c+(j xj − s)2/(j(j−1))
+renvoyer c/n
+*/
+
+
+
 /* ---------------------------------------------------------------- */
 /*
  *	more elaborate functions are in fimg-2gray.c