ExponentialVariogram.cpp

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#ifdef HAVE_CONFIG_H
   #include <config.h>
#else
#error "Cannot compile with HAVE_CONFIG_H symbol! run configure first!"
#endif
 
#include "../classes.h"
#include "../../shared/shared.h"
 
/*ExponentialVariogram constructors and destructor*/
ExponentialVariogram::ExponentialVariogram(){/*{{{*/
   this->nugget = 0.2;
   this->sill   = 1;
   this->range  = SQRT3;
   return;
}
/*}}}*/
ExponentialVariogram::ExponentialVariogram(Options* options){/*{{{*/
 
   /*Defaults*/
   this->nugget = 0.2;
   this->sill   = 1;
   this->range  = SQRT3;
 
   /*Overwrite from options*/
   if(options->GetOption("nugget")) options->Get(&this->nugget,"nugget");
   if(options->GetOption("sill"))   options->Get(&this->sill,"sill");
   if(options->GetOption("range"))  options->Get(&this->range,"range");
 
   /*Checks*/
   if(nugget==sill) _error_("nugget and sill cannot be equal (constant semivariogram not allowed)");
}
/*}}}*/
ExponentialVariogram::~ExponentialVariogram(){/*{{{*/
   return;
}
/*}}}*/
 
/*Object virtual functions definitions:*/
Object* ExponentialVariogram::copy(void){/*{{{*/
      return new ExponentialVariogram(*this);
}
/*}}}*/
void ExponentialVariogram::Echo(void){/*{{{*/
   _printf_("ExponentialVariogram\n");
   _printf_("   nugget: " << this->nugget << "\n");
   _printf_("   sill  : " << this->sill << "\n");
   _printf_("   range : " << this->range << "\n");
}
/*}}}*/
 
/*Variogram function*/
double ExponentialVariogram::Covariance(double deltax,double deltay){/*{{{*/
   /*The covariance can be deduced from the variogram from the following
    * relationship:
    *    2 gamma = C(x,x) + C(y,y) -2 C(x,y)
    * so
    *    C(h) = sill - gamma                                            */
   double h,a,cova;
 
   /*Calculate length*/
   h=sqrt(deltax*deltax + deltay*deltay);
 
   /*If h is too small, return sill*/
   if(h<0.0000001) return sill;
 
   /*compute covariance*/
   a     = 1./3.;
   cova = (sill-nugget)*exp(-h/(a*range));
   return cova;
}
/*}}}*/
double ExponentialVariogram::SemiVariogram(double deltax,double deltay){/*{{{*/
   /*http://en.wikipedia.org/wiki/Variogram*/
   double h,a,gamma;
 
   /*Calculate length*/
   h=sqrt(deltax*deltax + deltay*deltay);
 
   /*return semi-variogram*/
   a     = 1./3.;
   gamma = (sill-nugget)*(1-exp(-h/(a*range))) + nugget;
   return gamma;
}
/*}}}*/