--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rDiff/src/locfit/m/spence21.m	Thu Feb 14 23:38:36 2013 -0500
@@ -0,0 +1,27 @@
+function yhat=spence21(y)
+% function for Spencer's 21-point graduation rule.
+% set out following Spencer's hand-calculation method,
+% which isn't the shortest computer program!
+
+oten = ones(10,1);
+n = length(y);
+y = [ oten*y(1); y; oten*y(n) ];
+
+n = length(y);
+k = 4:(n-3);
+y1 = -y(k-3) + y(k-1) + 2*y(k) + y(k+1) -y(k+3);
+
+n = length(y1);
+k = 4:(n-3);
+y2 = y1(k-3)+y1(k-2)+y1(k-1)+y1(k)+y1(k+1)+y1(k+2)+y1(k+3);
+
+n = length(y2);
+k = 3:(n-2);
+y3 = y2(k-2)+y2(k-1)+y2(k)+y2(k+1)+y2(k+2);
+
+n = length(y3);
+k = 3:(n-2);
+y4 = y3(k-2)+y3(k-1)+y3(k)+y3(k+1)+y3(k+2);
+
+yhat = y4/350;
+return;