/*
   Template for a User fit function.
   Calculates a polynomial of degree 1 (i.e. a straight line).

   The user function should return one of the following return codes,
   defined in the include file "fitusr.h":

   number of function parameters   if FITFCT_NPAR
   FITUSR_OK                       if all OK, deriv.s are provided  
   FITUSR_NODERIV                  if all OK, deriv.s are not provided   
   FITUSR_SYS                      run time system error (e.g. calloc() failed) 
   FITUSR_UNPHYSICAL               unphysical region entered  
   FITUSR_OFLOFCT                  function not calculable    
   FITUSR_OFLODERIV                derivatives not calculable 

   /mk/ 

   $Log: usrfct.txt,v $
   Revision 1.2  2005/12/16 11:09:44  kraemer
   MacOSX (darwin) support added

   Revision 1.1  2005/11/11 10:10:56  kraemer
   *** empty log message ***

   $Id: usrfct.txt,v 1.2 2005/12/16 11:09:44 kraemer Exp $
  
*/

#include "fitusr.h"

#define DDPAR(iPar,iX) ddPar[ (iPar) * nX + (iX) ]
int usrfct( void *pFitFct,
            double *dPar,                  /* function parameters */
            double *ddPar,                 /* switch=FITFCT_VAL:
                                              ddPar[iPar*2+0] = lower limit
                                              ddPar[iPar*2+1] = upper limit
                                              switch=FITFCT_DERIV:
                                              ddPar[nPar*nX+iX]
                                              switch=else
                                              ddPar undefined
                                           */
            double *dX, double *dY,
            int nPar, int nX, int iSwitch ) {
   int iRC = FITUSR_OK;                            /* return code */
   int ii;

   switch( iSwitch ) {
   case FITFCT_NPAR:      /* return # of parameters */
      iRC = 2;
   break;
   case FITFCT_VAL:       /* return start values    */
      dPar[0] = 0E0;
      dPar[1] = 0E0;
      ddPar[0*2+0] = -1E6;    /* lower limit first parameter */
      ddPar[0*2+1] =  1E6;    /* upper limit first parameter */
      ddPar[1*2+0] = -1E6;    /* lower limit second parameter */
      ddPar[1*2+1] =  1E6;    /* upper limit second parameter */
   break;
   case FITFCT_FCT:       /* return function values only */
   case FITFCT_DISP:      /* return function values only, for display */
   case FITFCT_RESULT:    /* function is called for computation of results */
      for ( ii=0; ii<nX; ii++ ) {
         dY[ii] = dPar[1] * dX[ii] + dPar[0];
      }
   break;
   case FITFCT_DERIV:     /* return function values & parameter derivatives  */
      for ( ii=0; ii<nX; ii++ ) {
         dY[ii] = dPar[1] * dX[ii] + dPar[0];
                          /* first parameter derivative at x[ii] */
         ddPar[0*nX+ii] = 1E0;
                          /* second parameter derivative at x[ii] */
         ddPar[1*nX+ii] = dX[ii];
      }
      iRC = FITUSR_OK;    /* deriv.s are returned,
                             use FITUSR_NODERIV if no deriv.s are returned*/
   break;
   case FITFCT_CLEANUP:   /* function is called to allow cleanup */
   break;
   default: break;
   }
   return(iRC);
}