Java Integration Help

**CWalrus** · October 3rd, 2014, 01:42 PM

Hey I am working on this program to aproximate the integral of the function sin(x)/x using Reimann sums (left hand). It is close, but whenever I try to check it in the web grader some of my results are way off. Any help is apreciated. Here is my code.

public class Integrate {
	public static void main(String[] args) {
		if (args.length != 3) {
			System.out.println("Error: must enter a, b, n");
			System.exit(1);
		}
		double a=Double.parseDouble(args[0]);
		double b=Double.parseDouble(args[1]);
		double n=Double.parseDouble(args[2]);
		double h = ((b-a)/n);
		double result=0;
		for (int i=0;i<n;i++) {
			double x=(a+(i*h));
			double aprox = ((Math.sin(x)/x)*h);
			result=result+aprox;
		}
		System.out.printf("Sine =~ %.5f", result);
	}
}

**GregBrannon** · October 3rd, 2014, 01:42 PM

Same thing. Post your code correctly.

**CWalrus** · October 3rd, 2014, 01:45 PM

Sorry about posting my code incorrectly.

**GregBrannon** · October 3rd, 2014, 01:59 PM

Can you show the results of the web grader? Copy and paste them into a post, if possible.

Oh, and what are 'a', 'b', and 'n'? Can you give some examples?

**CWalrus** · October 3rd, 2014, 02:08 PM

These web grader results are actually for a nearly identical program in C. Left is the expected result, right is what I get.
integral of sin(x)/x on [-6.280000, 6.280000] ~= 2.836724 I got -nan
integral of sin(x)/x on [3.150000, 6.000000] ~= -0.427175 I got -0.423824
integral of sin(x)/x on [5.000000, 10.000000] ~= 0.105794 I got 0.105794
integral of sin(x)/x on [-2.900000, -0.001000] ~= 1.840776 I got 1.605243
integral of sin(x)/x on [0.000000, 1.000000] ~= 0.960932 I got -nan
integral of sin(x)/x on [0.000000, 3.140000] ~= 1.852094 I got -nan

And I made a mistake in the original post, i should go from zero to n-1, not from 1 to n. I am fixing that now.

**GregBrannon** · October 3rd, 2014, 02:13 PM

This doesn't look right:

double a=Double.parseDouble(args[0]);
double b=Double.parseDouble(args[0]);
double n=Double.parseDouble(args[0]);

Why are all args[0]?

**CWalrus** · October 3rd, 2014, 02:23 PM

haha I don't know why that was like that. Obviously they were supposed to be args[0], args[1], and args[2]. That was not a problem in the original program, and I have fixed it now. Sorry about that.

**GregBrannon** · October 3rd, 2014, 04:08 PM

As Norm pointed out, your threads are primarily math based, probably meant to explore math concepts rather than Java concepts (we might have programmed them in MATLAB or Fortran), and you haven't provided us much info about what they're supposed to do and how they're supposed to do it. (Code comments would be nice.)

Perhaps a math major will come by and find your topics interesting, but to be much help the rest of us would have to fill in our knowledge gaps that your subjects have revealed.

Be patient for that excited math major to come by.

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