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package bisection;
/*
* Benjamin Culkin
* 1/16/2018
* CS 479
* Bisection
*
* Use the bisection method to find bracketed roots of arbitrary real-valued functions.
*/
import java.util.function.DoubleUnaryOperator;
public class PreBisection {
public static void main(String[] args) {
// The functions we're approximating a root for
DoubleUnaryOperator functionA = x -> Math.cos(x) - x;
DoubleUnaryOperator functionB = x -> {
double valA = Math.pow(x, 5);
double valB = 3 * Math.pow(x, 4);
double valC = 4 * Math.pow(x, 3);
return valA - valB + valC - 1;
};
DoubleUnaryOperator functionC = x -> (x * x) - 3;
// The approximated roots
double answerA = bisect(functionA, 0, 1, 0.0001);
double answerB = bisect(functionB, 0, 1, 0.0001);
double answerC = bisect(functionC, 1, 2, 0.0000001);
// Print out the answers + their function
System.out.printf("x = cos(x) => %.4f\n", answerA);
System.out.printf("x^5 - 3x^4 + 4x^2 - 1 => %.4f\n", answerB);
System.out.printf("x^2 - 3 => %.7f\n", answerC);
}
// Calculate the number of iterations to approximate to a specified tolerance
private static double iterCount(double a, double b, double tol) {
double inside = Math.log((b - a) / tol);
return Math.ceil(inside / Math.log(2));
}
// Calculate a root for an equation by the bisection method
private static double bisect(DoubleUnaryOperator func, double a, double b, double tol) {
// Calculate the number of iterations
double N = iterCount(a, b, tol);
double val = 0.0;
// Set our values
double newa = a;
double newb = b;
double newc = (a + b) / 2;
// Continue onwards until we get the approximation to within the right tolerance
for (int i = 0; i < N; i++) {
newc = (newa + newb) / 2;
val = func.applyAsDouble(newc);
// Pick the right direction to bisect in
if (func.applyAsDouble(newa) * val < 0) {
newb = newc;
} else {
newa = newc;
}
}
// Return the right value
return newc;
}
}
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