PATCH for cond()

[Ben Abbott]

I've attached a patch respecting Rolf's change to cond().

	2008-02-08  Rolf Fabian <r fabian at jacobs-university dot de>

	* linear-algebra/cond.m: Changed to respect a second argument used to
	optionally specify 1-norm, inf-norm, or frobenius-norm. 
 

--- /Users/bpabbott/Development/cvs/octave/scripts/linear-algebra/cond.m	2008-01-22 16:52:25.000000000 -0500
+++ cond.m	2008-02-08 09:59:38.000000000 -0500
@@ -1,5 +1,5 @@
 ## Copyright (C) 1993, 1994, 1995, 1996, 1997, 1999, 2000, 2003, 2004,
-##               2005, 2006, 2007 John W. Eaton
+##               2005, 2006, 2007, 2008 John W. Eaton
 ##
 ## This file is part of Octave.
 ##
@@ -18,37 +18,49 @@
 ## <http://www.gnu.org/licenses/>.
 
 ## -*- texinfo -*-
-## @deftypefn {Function File} {} cond (@var{a})
-## Compute the (two-norm) condition number of a matrix. @code{cond (a)} is
-## defined as @code{norm (a) * norm (inv (a))}, and is computed via a
-## singular value decomposition.
-## @seealso{norm, svd, rank}
+## @deftypefn {Function File} {} cond (@var{a}, at var{p})
+## Compute the @var{p}-norm condition number of a matrix. @code{cond (@var{a})} is
+## defined as @code{norm (@var{a}, @var{p}) * norm (inv (@var{a}), @var{p})}.
+## By default @code{@var{p}=2} is used which implies a (relatively slow)
+## singular value decomposition. Other possible selections are 
+## @code{@var{p}= 1, Inf, inf, 'Inf', 'fro'} which are generally faster.
+## @seealso{norm, inv, det, svd, rank}
 ## @end deftypefn
 
 ## Author: jwe
 
-function retval = cond (a)
+function retval = cond (a,p)
 
-  if (nargin == 1)
+  if (nargin && nargin < 3)
     if (ndims (a) > 2)
       error ("cond: Only valid on 2-D objects")
     endif
 
-    [nr, nc] = size (a);
-    if (nr == 0 || nc == 0)
-      retval = 0.0;
+    if (nargin <2)
+      p = 2;
     endif
-    if (any (any (isinf (a) | isnan (a))))
-      error ("cond: argument must not contain Inf or NaN values");
+
+    if (!isstr(p) && p == 2)
+       [nr, nc] = size (a);
+       if (nr == 0 || nc == 0)
+           retval = 0.0;
+           return;
+       endif
+
+       if (any (any (isinf (a) | isnan (a))))
+          error ("cond: argument must not contain Inf or NaN values");
+       else
+          sigma   = svd (a);
+          sigma_1 = sigma(1);
+          sigma_n = sigma(end);
+          if (sigma_1 == 0 || sigma_n == 0)
+             retval = Inf;
+          else
+             retval = sigma_1 / sigma_n;
+          endif
+       endif
     else
-      sigma = svd (a);
-      sigma_1 = sigma(1);
-      sigma_n = sigma(length (sigma));
-      if (sigma_1 == 0 || sigma_n == 0)
-        retval = Inf;
-      else
-        retval = sigma_1 / sigma_n;
-      endif
+       retval = norm (a, p) * norm (inv (a), p);  
     endif
   else
     print_usage ();
@@ -56,11 +68,20 @@
 
 endfunction
 
-%!assert(abs (cond ([1, 2; 2, 1]) - 3) < sqrt (eps));
+%!test
+%! y= [7, 2, 3; 1, 3, 4; 6, 4, 5];
+%! tol = 1e-6;
+%! type = {1, 2, 'fro', 'inf', inf};
+%! for n = 1:numel(type)
+%!   rcondition(n) = 1 / cond (y, type{n});
+%! endfor
+%! assert (rcondition, [0.017460, 0.019597, 0.018714, 0.012022, 0.012022], tol);
+
+%!assert (abs (cond ([1, 2; 2, 1]) - 3) < sqrt (eps));
 
-%!assert(cond ([1, 2, 3; 4, 5, 6; 7, 8, 9]) > 1.0e+16);
+%!assert (cond ([1, 2, 3; 4, 5, 6; 7, 8, 9]) > 1.0e+16);
 
 %!error cond ();
 
-%!error cond (1, 2);
+%!error cond (1, 2, 3);
 

-------------- next part --------------
A non-text attachment was scrubbed...
Name: cond.diff
Type: application/octet-stream
Size: 3129 bytes
Desc: not available
Url : https://www.cae.wisc.edu/pipermail/bug-octave/attachments/20080208/58611768/attachment.obj