[eiresult,x]=ei(x);

function [eiresult,x]=ei(x);
eiresult=[];
persistent ei ; 

if isempty(eiresult), eiresult=0; end;
%***BEGIN PROLOGUE  EI
%***PURPOSE  Compute the exponential integral Ei(X).
%***LIBRARY   SLATEC (FNLIB)
%***CATEGORY  C5
%***TYPE      SINGLE PRECISION (EI-S, DEI-D)
%***KEYWORDS  EI FUNCTION, EXPONENTIAL INTEGRAL, FNLIB,
%             SPECIAL FUNCTIONS
%***AUTHOR  Fullerton, W., (LANL)
%***DESCRIPTION
%
% EI calculates the single precision exponential integral, Ei(X), for
% positive single precision argument X and the Cauchy principal value
% for negative X.  If principal values are used everywhere, then, for
% all X,
%
%    Ei(X) = -E1(-X)
% or
%    E1(X) = -Ei(-X).
%
%***REFERENCES  (NONE)
%***ROUTINES CALLED  E1
%***REVISION HISTORY  (YYMMDD)
%   770401  DATE WRITTEN
%   891115  Modified prologue description.  (WRB)
%   891115  REVISION DATE from Version 3.2
%   891214  Prologue converted to Version 4.0 format.  (BAB)
%***end PROLOGUE  EI
%***FIRST EXECUTABLE STATEMENT  EI
eiresult = -e1(-x);
%
csnil=dbstack(1); csnil=csnil(1).name(1)~='@';
if csnil&&~isempty(inputname(1)), assignin('caller','FUntemp',x); evalin('caller',[inputname(1),'=FUntemp;']); end
end
%DECK EISDOC