Mercurial > hg > octave-lojdl
changeset 9094:2e35cfcf6a6a
fix, optimize & extend pascal
author | Jaroslav Hajek <highegg@gmail.com> |
---|---|
date | Mon, 06 Apr 2009 11:16:20 +0200 |
parents | 8be05554bbd0 |
children | b5a1a2d0be7e |
files | scripts/ChangeLog scripts/special-matrix/pascal.m |
diffstat | 2 files changed, 18 insertions(+), 7 deletions(-) [+] |
line wrap: on
line diff
--- a/scripts/ChangeLog +++ b/scripts/ChangeLog @@ -1,3 +1,7 @@ +2009-04-06 Jaroslav Hajek <highegg@gmail.com> + + * special-matrix/pascal.m: Fix, optimize & extend. + 2009-04-06 Jaroslav Hajek <highegg@gmail.com> * linear-algebra/vech.m: Optimize.
--- a/scripts/special-matrix/pascal.m +++ b/scripts/special-matrix/pascal.m @@ -1,4 +1,5 @@ ## Copyright (C) 1999, 2006, 2007 Peter Ekberg +## Copyright (C) 2009 VZLU Prague ## ## This file is part of Octave. ## @@ -23,6 +24,8 @@ ## @var{t} defaults to 0. Return lower triangular Cholesky factor of ## the Pascal matrix if @code{@var{t} = 1}. This matrix is its own ## inverse, that is @code{pascal (@var{n}, 1) ^ 2 == eye (@var{n})}. +## If @code{@var{t} = -1}, return its absolute value. This is the +## standard pascal triangle as a lower-triangular matrix. ## If @code{@var{t} = 2}, return a transposed and permuted version of ## @code{pascal (@var{n}, 1)}, which is the cube-root of the identity ## matrix. That is @code{pascal (@var{n}, 2) ^ 3 == eye (@var{n})}. @@ -44,18 +47,22 @@ t = 0; endif - if (! is_scalar (n) || ! is_scalar (t)) + if (! isscalar (n) || ! isscalar (t)) error ("pascal: expecting scalar arguments, found something else"); endif - retval = diag ((-1).^[0:n-1]); - retval(:,1) = ones (n, 1); + retval = zeros (n); + retval(:,1) = 1; - for j = 2:n-1 - for i = j+1:n - retval(i,j) = retval(i-1,j) - retval(i-1,j-1); + if (t == -1) + for j = 2:n-1 + retval(j:n,j) = cumsum (retval (j-1:n-1,j-1)); endfor - endfor + else + for j = 2:n-1 + retval(j:n,j) = -cumsum (retval (j-1:n-1,j-1)); + endfor + endif if (t == 0) retval = retval*retval';