      real function getz(pval,nt,vr,cdf,zmin,zmax,ltail,ltpar,
     +                   utail,utpar)
C%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
C                                                                      %
C Copyright (C) 1996, The Board of Trustees of the Leland Stanford     %
C Junior University.  All rights reserved.                             %
C                                                                      %
C The programs in GSLIB are distributed in the hope that they will be  %
C useful, but WITHOUT ANY WARRANTY.  No author or distributor accepts  %
C responsibility to anyone for the consequences of using them or for   %
C whether they serve any particular purpose or work at all, unless he  %
C says so in writing.  Everyone is granted permission to copy, modify  %
C and redistribute the programs in GSLIB, but only under the condition %
C that this notice and the above copyright notice remain intact.       %
C                                                                      %
C%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
c-----------------------------------------------------------------------
c
c           Back Transform Univariate Data from Normal Scores
c           *************************************************
c
c This subroutine backtransforms a standard normal deviate from a
c specified back transform table and option for the tails of the
c distribution.  Call once with "first" set to true then set to false
c unless one of the options for the tail changes.
c
c
c
c INPUT VARIABLES:
c
c   pval             probability value to use
c   nt               number of values in the back transform tbale
c   vr(nt)           original data values that were transformed
c   cdf(nt)          the corresponding transformed values
c   zmin,zmax        limits possibly used for linear or power model
c   ltail            option to handle values less than cdf(1)
c   ltpar            parameter required for option ltail
c   utail            option to handle values greater than cdf(nt)
c   utpar            parameter required for option utail
c
c
c
c-----------------------------------------------------------------------
      parameter(EPSLON=1.0e-20)
      dimension vr(nt),cdf(nt)
      real      ltpar,utpar,lambda
      integer   ltail,utail
c
c Value in the lower tail?    1=linear, 2=power, (3 and 4 are invalid):
c
      if(pval.le.cdf(1)) then
                  getz = vr(1)
            if(ltail.eq.1) then
                  getz = powint(0.0,cdf(1),zmin,vr(1),pval,1.0)
            else if(ltail.eq.2) then
                  cpow = 1.0 / ltpar
                  getz = powint(0.0,cdf(1),zmin,vr(1),pval,cpow)
            endif
c
c Value in the upper tail?     1=linear, 2=power, 4=hyperbolic:
c
      else if(pval.ge.cdf(nt)) then
                  cdfhi  = cdf(nt)
                  getz   = vr(nt)
            if(utail.eq.1) then
                  getz   = powint(cdfhi,1.0,vr(nt),zmax,pval,1.0)
            else if(utail.eq.2) then
                  cpow   = 1.0 / utpar
                  getz   = powint(cdfhi,1.0,vr(nt),zmax,pval,cpow)
            else if(utail.eq.4) then
                  lambda = (vr(nt)**utpar)*(1.0-cdf(nt))
                  getz   = (lambda/(1.0-pval))**(1.0/utpar)
            endif
      else
c
c Value within the transformation table:
c
            call locate(cdf,nt,1,nt,pval,j)
            j    = max(min((nt-1),j),1)
            getz = powint(cdf(j),cdf(j+1),vr(j),vr(j+1),pval,1.0)
      endif
      if(getz.lt.zmin) getz = zmin
      if(getz.gt.zmax) getz = zmax
      return
      end
