polyfit: add a third output argument, mu [PATCH]

[Shaun Jackman]

The following patch adds a third output argument, mu for compatibility with 
Matlab. I made an effort to update the documentation, but I'm not familiar with 
Octave's documentation system.

Cheers,
Shaun

2008-06-30  Shaun Jackman  <address@hidden>

        * polynomial/polyfit.m (polyfit): Add a third output argument,
        mu, for compatibility. If three output arguments are requested,
        the input argument x is shifted and scaled before fitting.

--- /opt/octave-3.0.1/share/octave/3.0.1/m/polynomial/polyfit.m.orig	2008-04-25 
09:17:07.000000000 -0700
+++ /opt/octave-3.0.1/share/octave/3.0.1/m/polynomial/polyfit.m	2008-06-30 
11:15:46.000000000 -0700
@@ -51,6 +51,10 @@
 ## @item yf
 ## The values of the polynomial for each value of @var{x}.
 ## @end table
+##
+## If three output arguments are requested, the input argument @var{x}
+## is transformed before fitting by @code{(x - mu(1)) / mu(2)},
+## where @code{mu(1) = mean(x)} and @code{mu(2) = std(x)}.
 ## @end deftypefn

 ## Author: KH <address@hidden>
@@ -72,6 +76,12 @@
     error ("polyfit: n must be a nonnegative integer");
   endif

+  if (nargout > 2)
+         mu(1) = mean(x);
+         mu(2) = std(x);
+         x = (x - mu(1)) / mu(2);
+  endif
+
   y_is_row_vector = (rows (y) == 1);

   l = length (x);