/** A class to calculate summations and numeric integrals. The
* integral is calculated according to the midpoint rule.
*
* Taken from Core Web Programming from
* Prentice Hall and Sun Microsystems Press,
* http://www.corewebprogramming.com/.
* © 2001 Marty Hall and Larry Brown;
* may be freely used or adapted.
*/
public class Integral {
/** Returns the sum of f(x) from x=start to x=stop, where the
* function f is defined by the evaluate method of the
* Evaluatable object.
*/
public static double sum(double start, double stop,
double stepSize,
Evaluatable evalObj) {
double sum = 0.0, current = start;
while (current <= stop) {
sum += evalObj.evaluate(current);
current += stepSize;
}
return(sum);
}
/** Returns an approximation of the integral of f(x) from
* start to stop, using the midpoint rule. The function f is
* defined by the evaluate method of the Evaluatable object.
*/
public static double integrate(double start, double stop,
int numSteps,
Evaluatable evalObj) {
double stepSize = (stop - start) / (double)numSteps;
start = start + stepSize / 2.0;
return(stepSize * sum(start, stop, stepSize, evalObj));
}
}