Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / specfun-1.1.0 / Si.m

diff --git a/octave_packages/specfun-1.1.0/Si.m b/octave_packages/specfun-1.1.0/Si.m
new file mode 100644 (file)
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+++ b/octave_packages/specfun-1.1.0/Si.m
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+## Copyright (C) 2006   Sylvain Pelissier   <sylvain.pelissier@gmail.com>
+##
+## This program is free software; you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation; either version 3 of the License, or
+## (at your option) any later version.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with this program; If not, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {@var{y} =} Si (@var{x})
+## Compute the sine integral defined by:
+## @verbatim
+##                    x
+##                   /
+##           Si(x) = | sin(t)/t dt
+##                   /
+##                   0
+## @end verbatim
+## @end deftypefn
+
+function y = Si(x)
+  if (nargin != 1)
+    print_usage;
+  endif
+  y = zeros(size(x));
+  if prod(size(x)) < 101
+    for k = 1:prod(size(x))
+      y(k) = sum(besselj([0:100]+0.5,(x(k)/2)).^2);
+    endfor
+    y = y.*pi;
+  else
+    for k=0:100
+      y += besselj(k+0.5,x/2).^2;
+    endfor
+    y = y.*pi;
+  endif
+endfunction