I am trying to compile a very complicated code and I get the error
g++ -o MCBody MCBody.cpp
MCBody.cpp:36:34: error: expected initializer before ‘<’ token
double numericalIntegration::pair<double,double> integrate(double (*pFun)(const double & x),const double & LBound, const double & UBound)
You can see that here is a problem with the recognition of the C++ pair object. I am too stupid to see what is wrong and cannot make the code very smaller. I want your help with respect.
Here is MCBody.cpp (the big one):
//---MCBody---//
// Function that performs a regular numeric integration by with random
// spacing between points and unit weighting. Tells the
// NumericalIntegration class what the functions are to do.
// INPUTS (for integrate):
// Fun = a function of x
// LBound = lower bound of integral
// UBound = upper bound of integral
// OUTPUT:
// IntDev = a pair with the first value being the integral and the second
// being the standard deviation.
#ifndef MCRULE_CPP // If Monte Carlo rule is not
#define MCRULE_CPP // defined, define it.
#include "NumericalIntegrationClass.h" // So it can see the class def.
#include <stdlib.h> // For rand and srand
#include <time.h> // Get random srand values.
#include <iostream>
#include <math.h>
#include <utility>
using namespace std;
// I: Tell the integration what the number of intervals/points taken are.
numericalIntegration::numericalIntegration(const int & numIntervals)
{
// THIS is a pointer to the current object within a member function. It
// is used when no other object name is specified.
this->numIntervals = numIntervals; // Stores the value of the
// parameter numIntervals.
}
// II: Perform the integration approximation.
double numericalIntegration::pair<double,double> integrate(double (*pFun)(const double & x),const double & LBound, const double & UBound)
{
// Return value is different to one stored in location pointed by time.
srand(time(NULL));
double XintSize = (UBound-LBound);
double Total = 0;
double SumOSquares = 0;
for (int i =0; i<=numIntervals; i++)
{
// Creating 'random' points within the lower bound and upper bound.
double x_i = LBound + (rand())/ (RAND_MAX/XintSize);
// Evaluate the pointer at x_i and add to Total.
double fx = (*pFun)(x_i);
Total += fx;
SumOSquares += pow(fx,2);
}
double Deviation = SumOSquares - pow(Total,2);
Deviation = (sqrt(Deviation))/((float)numIntervals+1);
double Integral = (1/((float)numIntervals+1))*XintSize*Total;
pair<double,double> IntDev;
IntDev = make_pair(Integral,Deviation);
return IntDev;
}
#endif
Here is MCRule.cpp:
//---MCRule---//
// A function to calculate the integral of a function via the Monte Carlo
// method.
// INPUTS:
// n = number of points
// l = lower limit of the integration
// u = upper limit of the integration
// line 24: the function to be integrated
// I: Define a function that is supposed to be integrated.
#include "NumericalIntegrationClass.h" // Want to include a reference to
// the header in the main file so
// it can see what's happening in
// the class.
#include <math.h> // Cos.
#include "MCBody.cpp"
#include <iostream>
#include <utility>
double fun(const double & x) // Passing a reference to some number x
{ // (not going to change x within the loop).
// Passing by reference, therefore not
// allocating any new space.
// Define the function to be integrated.
return ((1 + 0.25*cos(x))/(1+x*x));
//return (1+0.25*cos(tan(x)));
}
// II: Execute Monte Carlo integration function.
int main (int argc, char* argv[]) // First bit = counts the arguments.
// Sec bit = the vector that stores the
// arguments.
{
// Retrieve inputs.
int n = atoi(argv[1]); // Extracts number of points.
double l = atoi(argv[2]); // Extracts lower bound for integration.
double u = atoi(argv[3]); // Extracts upper bound for integration.
// Define number of intervals.
numericalIntegration numInt(n);
// Define lower and upper bounds for integral.
pair<double,double> IntDev = numInt.integrate(fun,l,u);
float abso = fabs(IntDev.first - 3.2294), rel = (abso/IntDev.first)*100;
cout << "Integral is: " << IntDev.first << endl;
cout << "Absolute Error: " << abso << endl;
cout << "Relative Error: " << rel << "%" << endl;
cout << "Standard Deviation: " << IntDev.second << endl;
cout << "Monte Carlo Error: " << IntDev.second/(sqrt(n+1)) << endl;
return 0;
}
Here is NumericalIntegrationClass.h:
//---NumericalIntegrationClass---//
// Creates a class of for functions which can be integrated using the
// Monte Carlo method.
// This class has 2 public functions; one which points the class to the
// number of points/intervals used (numericalIntegration), and one used
// to perform the actual integration approximation.
// I: PRE-PROCESSORS
#pragma once // Current source file to be included once in a single
// compilation. Serves same purpose of #include guard but
// avoids name clashes.
#include <utility>
using namespace std;
class numericalIntegration
{
// II: DEFINE PUBLIC
// Public area can be touched from outside of the function.
public:
// NUMERICALINTEGRATION: Setting the number of intervals to be a
// constant integer.
numericalIntegration(const int & numIntervals);
// INTEGRATE: Call the method that calculates the value of the
// integral.
pair<double,double> integrate(double (*pFun)(const double & x),const double & LBound, const double & UBound);
// III: DEFINE PRIVATE
// Private area can only be touched by internal methods.
private:
int numIntervals;
};
numericalIntegration::pair<double,double>
This means:
numericalIntegration classpair member<double, double> argumentsThis fails at #2 as there is no pair member in numericalIntegration. There is a member named integrate that returns std::pair<double, double>. To express that in C++, you say
pair<double,double> numericalIntegration::integrate