expDist.cpp

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#include "expDist.h"
#include <cmath>
#include <iostream>

/*
    Exponential Distribution Class
    
    This class was created to allow the user to specify
    the min and max values received from the exponential
    distrubution function.
*/

/***************************************************************************/
/**************************** Constructor **********************************/
ExpDist::ExpDist(double maxDecimal, std::mt19937_64 &_generator) : generator(_generator) {
    maxInput = maxDecimal;
    generator = _generator;
}


/***************************************************************************/
/************** Random Uniform Random Number Generator *********************/
double ExpDist::unifRandom(double min, double max) {
    return ((max-min) *  double(generator())/generator.max() + min);
}


/***************************************************************************/
/***************************************************************************/
// Overloaded Function
double ExpDist::getValue(double lambda, double rv) {
    
    if (rv > 1) { 
       std::cout << "ERROR: Attempted to input random value of greater than 1 to the exponential " 
                 << "distribution class's getValue() function. Input must be on [0,1] interval.\n";
       exit(1);
   }
    
   // Using inverse CDF
   if (rv != 1) { 
       return  -std::log(1-rv)/lambda;
   }
   else {
       return -std::log(1-maxInput)/lambda;
   }
}


/***************************************************************************/
/***************************************************************************/
// Overloaded Function
double ExpDist::getValue(double lambda, double minVal, double maxVal) {
    // Uniform distrubution on [minVal, maxVal)
    if ( maxVal > 1 || minVal > 1) { 
        // Passing 1 into exp. distribution will reuturn inf
        std::cout << "ERROR: Passed min, or max, input value of greater than 1 to getValue()" 
                  << " in expDist.cpp. Input must be in [0,1] interval.\n";
        exit(1);
    }

   double randVar = unifRandom(minVal, maxVal);
 
   // Using inverse CDF
   // If randVar is 1, this function returns inf
   if (randVar != 1) { 
       return  -std::log(1-randVar)/lambda;
   }
   else {
       return -std::log(1-maxInput)/lambda;
   }          
}


/***************************************************************************/
/*******************  Get Max Value Possible  ******************************/
double ExpDist::getMaxValue(double lambda) {
        return -std::log(1-maxInput)/lambda;
}


/***************************************************************************/
/*********  Compute Input to Distribution for a Certain Output  ************/
double ExpDist::computeInput(double output, double lambda) {
   return 1.0 - std::exp(-lambda*output);
}