From octave-sources-request at bevo dot che dot wisc dot edu  Sun Dec 17 10:03:57 2000
Subject: special function e_1 ( exponential function )
From: karas <karas at gollum dot uci dot agh dot edu dot pl>
To: octave-sources at bevo dot che dot wisc dot edu
Date: 17 Dec 2000 17:07:43 -0100

file : e1.m
-- 
## Copyright (C) 2000, Wojciech Kara‚¶
## 
## 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, 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 file.  If not, write to the Free Software Foundation,
## 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

## usage:  e1(x)
##
## Computes the exponential function e_1(x) ( see M.Abramowitz, I.Stegun, 
## Dover Publications,Inc., 1972, &&5.1.53,51.55, p.231 )
## Precision 0<=x<=1    => 2e-7
##           1<=x<=INF  => 2e-8 

  
## Author: WK <karas at uci dot agh dot edu dot pl>
## Created: 17 December 2000

function ret = e1(x)
 if ( x <= 1.0 )
     ret = -log(x)-.57721566+x*(.99999193+x*(-.24991055+x*(.05519968+x*(-.00976004+x*.00107857))))
 else
     nom = .2677737343+x*(8.6347608925+x*(18.0590169730+x*(8.5733287401+x)))
     den = 3.9584969228+x*(21.0996530827+x*(25.6329561486+x*(9.5733223454+x)))
     ret = exp(-x)/x
     ret = ret*(nom/den)
 endif
endfunction

W.Karas
mailto:karas at uci dot agh dot edu dot pl
http://gollum.uci.agh.edu.pl



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