#include "TrapeziodalIntegration.h"
#include "myFunction.h"

double TrapezoidalArea(double startX, double endX, int nSubIntervals)
{

  double dx = (endX - startX)/nSubIntervals;

  double yi[nSubIntervals + 1]; 
  
  for(int index=0; index<=nSubIntervals; index++)
    yi[index] = myFunction(startX + index*dx);

  double sum = yi[0] / 2.0;           // initialize sum to 1/2 of f(startX)
  
  for(int j = 1; j < nSubIntervals; j++) 
    sum += yi[j];                     // add f(xi) to sum
 
  sum += yi[nSubIntervals] / 2.0;     // add 1/2 of f(endX) to sum
  
  return dx * sum;                    // total area of trapezoids
}