/* 	Exhf.java
	
	Explicit heat flow equation, finite differenced.
	Adapted from Jon Claerbout's Imaging the Earth's Interior (1985), p. 94,
	by John N. Louie, 28 November 1998.
*/

/* Include the usual classes */
import java.util.*;
import java.io.*;
import java.lang.Math;

/* Declare a class with a main() method to contain the finite-difference code. */
/* When you change the code in this file, make a copy to a new file with
    a new name like "ex6exhf.java", and be sure to make the same change
    to the class name below - e.g. "class ex6exhf" */
class exhf
	{
	/* The main() method compiles into a file named "exhf.class" that
	    you run in the Java virtual machine as a stand-alone application
	    with a command such as "java exhf"; or however you have
	    renamed it. */
	public static void main(String args[]) /* No runtime arguments needed */
		{
		System.out.println("Starting exhf...");
		/* Declare variables */
		int nx, ia, it, ix;
		float alpha, q[], qp[];
		/* Dimension arrays */
		nx = 12;
		q = new float[nx];
		qp = new float[nx];
		
		/* Loop through a stable and an unstable case */
		for (ia=0; ia<2; ia++)
			{
			alpha = 0.333F*(ia+1);
			System.out.println("alpha = " + alpha);
	
			/* Initial temperature is a step function in x */
			for (ix=0; ix<6; ix++)
				q[ix] = 0F;
			for (ix=6; ix<12; ix++)
				q[ix] = 1F;
	
			/* Iterate in time */
			for (it=0; it<6; it++)
				{
				/* Print current state of array */
				for (ix=0; ix<nx; ix++)
					System.out.print(" " + q[ix]);
				System.out.println("");
	
				/* Apply differencing star to array */
				for (ix=1; ix<nx-1; ix++)
					qp[ix] = q[ix]
						 + alpha*(q[ix-1] - 2F*q[ix] + q[ix+1]);
					
				/* Set side boundaries */
				qp[0] = qp[1];
				qp[nx-1] = qp[nx-2];
	
				/* Assign original array to new time step */
				for (ix=0; ix<nx; ix++)
					q[ix] = qp[ix];
				}
			/* Print some space between the cases */
			System.out.println("");
			}
		/* End of exhf's main() application method. */
		}
	/* End of methods in class exhf */
	}