00001 #include "cdflib.h"
00002 void dstinv(double *zsmall,double *zbig,double *zabsst,
00003             double *zrelst,double *zstpmu,double *zabsto,
00004             double *zrelto)
00005 /*
00006 **********************************************************************
00007       void dstinv(double *zsmall,double *zbig,double *zabsst,
00008             double *zrelst,double *zstpmu,double *zabsto,
00009             double *zrelto)
00010 
00011       Double Precision - SeT INverse finder - Reverse Communication
00012                               Function
00013      Concise Description - Given a monotone function F finds X
00014      such that F(X) = Y.  Uses Reverse communication -- see invr.
00015      This routine sets quantities needed by INVR.
00016           More Precise Description of INVR -
00017      F must be a monotone function, the results of QMFINV are
00018      otherwise undefined.  QINCR must be .TRUE. if F is non-
00019      decreasing and .FALSE. if F is non-increasing.
00020      QMFINV will return .TRUE. if and only if F(SMALL) and
00021      F(BIG) bracket Y, i. e.,
00022           QINCR is .TRUE. and F(SMALL).LE.Y.LE.F(BIG) or
00023           QINCR is .FALSE. and F(BIG).LE.Y.LE.F(SMALL)
00024      if QMFINV returns .TRUE., then the X returned satisfies
00025      the following condition.  let
00026                TOL(X) = MAX(ABSTOL,RELTOL*ABS(X))
00027      then if QINCR is .TRUE.,
00028           F(X-TOL(X)) .LE. Y .LE. F(X+TOL(X))
00029      and if QINCR is .FALSE.
00030           F(X-TOL(X)) .GE. Y .GE. F(X+TOL(X))
00031                               Arguments
00032      SMALL --> The left endpoint of the interval to be
00033           searched for a solution.
00034                     SMALL is DOUBLE PRECISION
00035      BIG --> The right endpoint of the interval to be
00036           searched for a solution.
00037                     BIG is DOUBLE PRECISION
00038      ABSSTP, RELSTP --> The initial step size in the search
00039           is MAX(ABSSTP,RELSTP*ABS(X)). See algorithm.
00040                     ABSSTP is DOUBLE PRECISION
00041                     RELSTP is DOUBLE PRECISION
00042      STPMUL --> When a step doesn't bound the zero, the step
00043                 size is multiplied by STPMUL and another step
00044                 taken.  A popular value is 2.0
00045                     DOUBLE PRECISION STPMUL
00046      ABSTOL, RELTOL --> Two numbers that determine the accuracy
00047           of the solution.  See function for a precise definition.
00048                     ABSTOL is DOUBLE PRECISION
00049                     RELTOL is DOUBLE PRECISION
00050                               Method
00051      Compares F(X) with Y for the input value of X then uses QINCR
00052      to determine whether to step left or right to bound the
00053      desired x.  the initial step size is
00054           MAX(ABSSTP,RELSTP*ABS(S)) for the input value of X.
00055      Iteratively steps right or left until it bounds X.
00056      At each step which doesn't bound X, the step size is doubled.
00057      The routine is careful never to step beyond SMALL or BIG.  If
00058      it hasn't bounded X at SMALL or BIG, QMFINV returns .FALSE.
00059      after setting QLEFT and QHI.
00060      If X is successfully bounded then Algorithm R of the paper
00061      'Two Efficient Algorithms with Guaranteed Convergence for
00062      Finding a Zero of a Function' by J. C. P. Bus and
00063      T. J. Dekker in ACM Transactions on Mathematical
00064      Software, Volume 1, No. 4 page 330 (DEC. '75) is employed
00065      to find the zero of the function F(X)-Y. This is routine
00066      QRZERO.
00067 **********************************************************************
00068 */
00069 {
00070     E0000(1,NULL,NULL,NULL,NULL,NULL,zabsst,zabsto,zbig,zrelst,zrelto,zsmall,
00071     zstpmu);
00072 } /* END */