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changeset 9104:e0250e2b60ed

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optimize vander
author Jaroslav Hajek <highegg@gmail.com>
date Wed, 08 Apr 2009 13:16:23 +0200
parents 10bed8fbec99
children 9b12ed1fbbbd
files scripts/ChangeLog scripts/special-matrix/vander.m
diffstat 2 files changed, 13 insertions(+), 1 deletions(-) [+]
line wrap: on
line diff
--- a/scripts/ChangeLog
+++ b/scripts/ChangeLog
@@ -1,3 +1,7 @@
+2009-04-08  Jaroslav Hajek  <highegg@gmail.com>
+
+	* special-matrix/vander.m: Optimize.
+
 2009-04-07  Ben Abbott <bpabbott@mac.com>
 
 	* plot/Makefile.in: Remove __gnuplot_default_font__.m from SOURCES.
--- a/scripts/special-matrix/vander.m
+++ b/scripts/special-matrix/vander.m
@@ -1,5 +1,6 @@
 ## Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2002,
 ##               2004, 2005, 2006, 2007, 2008, 2009 John W. Eaton
+## Copyright (C) 2009 VZLU Prague
 ##
 ## This file is part of Octave.
 ##
@@ -58,7 +59,14 @@
 
   if (isvector (c))
     n = length (c);
-    retval = (c(:) * ones (1, n)) .^ (ones (n, 1) * (n-1:-1:0));
+    retval = zeros (n, n, class (c));
+    ## avoiding many ^s appears to be faster for n >= 100.
+    d = 1;
+    c = c(:);
+    for i = n:-1:1
+      retval(:,i) = d;
+      d = c .* d;
+    endfor
   else
     error ("vander: argument must be a vector");
   endif