[acoshresult,x]=acosh(x);

function [acoshresult,x]=acosh(x);
acoshresult=[];
persistent acosh aln2 firstCall xmax ; if isempty(firstCall),firstCall=1;end; 

if isempty(acoshresult), acoshresult=0; end;
if isempty(aln2), aln2=0; end;
if isempty(xmax), xmax=0; end;
%***BEGIN PROLOGUE  ACOSH
%***PURPOSE  Compute the arc hyperbolic cosine.
%***LIBRARY   SLATEC (FNLIB)
%***CATEGORY  C4C
%***TYPE      SINGLE PRECISION (ACOSH-S, DACOSH-D, CACOSH-C)
%***KEYWORDS  ACOSH, ARC HYPERBOLIC COSINE, ELEMENTARY FUNCTIONS, FNLIB,
%             INVERSE HYPERBOLIC COSINE
%***AUTHOR  Fullerton, W., (LANL)
%***DESCRIPTION
%
% ACOSH(X) computes the arc hyperbolic cosine of X.
%
%***REFERENCES  (NONE)
%***ROUTINES CALLED  R1MACH, XERMSG
%***REVISION HISTORY  (YYMMDD)
%   770401  DATE WRITTEN
%   890531  Changed all specific intrinsics to generic.  (WRB)
%   890531  REVISION DATE from Version 3.2
%   891214  Prologue converted to Version 4.0 format.  (BAB)
%   900315  CALLs to XERROR changed to CALLs to XERMSG.  (THJ)
%   900326  Removed duplicate information from DESCRIPTION section.
%           (WRB)
%***end PROLOGUE  ACOSH
if firstCall,   aln2=[0.69314718055994530942e0];  end;
if firstCall,   xmax=[0.];  end;
firstCall=0;
%***FIRST EXECUTABLE STATEMENT  ACOSH
if( xmax==0. )
xmax = 1.0./sqrt(r1mach(3));
end;
%
if( x<1.0 )
xermsg('SLATEC','ACOSH','X LESS THAN 1',1,2);
end;
%
if( x<xmax )
acoshresult = log(x+sqrt(x.*x-1.0));
end;
if( x>=xmax )
acoshresult = aln2 + log(x);
end;
%
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 AIE