Integral Experiment in C

integral.c

/*
 * Brian Chrzanowski
 * Fri Jul 13, 2018 13:42
 *
 * perform integrals over any function that returns and takes a double
 * compile : cc integral.c -lm
 */

#include <stdio.h>
#include <math.h>

double integral(double(*f)(double x), double a, double b, int n);
double func_x_2(double x);
double func_x(double x);

int main(int argc, char **argv)
{
	printf("integral of cos %lf\n", integral(cos, 0, M_PI / 2, 1000));
	printf("integral of x^2 %lf\n", integral(func_x_2, 0, 4, 1000));
	printf("integral of x   %lf\n", integral(func_x, 0, 4, 1000));

	return 0;
}

/* what would this integral function that uses CUDA look like? */
double integral(double(*f)(double x), double a, double b, int n)
{
	int i;
	double step = (b - a) / n; // width of each small rectangle
	double area = 0.0;         // signed area

	for (i = 0; i < n; i++) {
		area += f(a + (i + 0.5) * step) * step; // sum up each rect
	}

	return area;
}

void cuda_integral(double(*f)(double x), double *arr, double a, double b)
{
	/*
	 * get each index, etc
	 */

	/* store each thread's output sum into arr*/

	/* 
	 * use shifts to move all the sums from 0...N positions,
	 * to the 0th position, where the intermediate positions are garbage
	 */
}

double func_x_2(double x)
{
	return x * x;
}

double func_x(double x)
{
	return x;
}