--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main/specfun/inst/Ci.m	Tue Oct 17 11:22:36 2006 +0000
@@ -0,0 +1,37 @@
+## Copyright (C) 2006   Sissou   <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 2 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, write to the Free Software
+## Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+
+## CI compute the cosine integral function define by:
+##
+##                    Inf
+##                   /
+##           Ci(x) = | cos(t)/t dt
+##                   /
+##                   x
+##
+##See also : cosint, Si, sinint, expint, expint_Ei.
+
+function y = Ci(z)
+	if (nargin != 1)
+		usage ("Ci(x)");
+	endif
+	y = z;
+	y(z == 0) = -Inf; 
+	y(real(z) == 0 & imag(z) >0)  = 0.5*(expint_Ei(i.*y(real(z) == 0 & imag(z) >0))+expint_Ei(-i.*y(real(z) == 0 & imag(z) >0)))+ i.*pi./2;
+	y(real(z) == 0 & imag(z) <0) = 0.5*(expint_Ei(i.*y(real(z) == 0 & imag(z) <0))+expint_Ei(-i.*y(real(z) == 0 & imag(z) <0)))-i*pi./2;
+	y(real(z)>0) = -0.5.*(expint_E1(i.*y(real(z)>=0) )+expint_E1(-i.*y(real(z)>=0) ));
+	y(real(z)<0) = -0.5.*(expint_E1(-i.*y(real(z)<0))+expint_E1(i.*y(real(z)<0)))+i*pi;
+endfunction;
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