/* From: "COMPUTATIONAL PHYSICS, 2nd Ed" 
   by RH Landau, MJ Paez, and CC Bordeianu 
   Copyright Wiley-VCH, 2007.
   Electronic Materials copyright: R Landau, Oregon State Univ, 2007;
   MJ Paez, Univ Antioquia, 2007; and CC Bordeianu, Univ Bucharest, 2007.
   Support by National Science Foundation                              
*/
// EqHeat.java: Solve heat equation via finite differences

import java.io.*;                                // Import IO library
                       
public class EqHeat  {                // Class constants in MKS units
	
  public static final int Nx = 11, Nt = 300;            // Grid sizes
  public static final double Dx = 0.01, Dt = 0.1;       // Step sizes
  public static final double KAPPA = 210.;    // Thermal conductivity
  public static final double SPH = 900.;             // Specific heat
  public static final double RHO = 2700.;               // Al density

  public static void main(String[] argv) 
                          throws IOException, FileNotFoundException {
														
    int ix, t;  
    double T[][] = new double[Nx][2];    
    double cons;   
		
    PrintWriter q = new PrintWriter               // File for gnuplot
                         (new FileOutputStream("EqHeat.dat"), true);
    for ( ix=1;  ix  <  Nx-1;  ix++ ) T[ix][0] = 100.;  // Initialize
    T[0][0] = 0.;           
		T[0][1] = 0.;                                     // Except ends
    T[Nx-1][0] = 0.;        
		T[Nx-1][1] = 0.; 
    cons = KAPPA/(SPH*RHO)*Dt/(Dx*Dx);          // Integration factor
    System.out.println("constant = " + cons);     
		                                                       // t loop
    for ( t=1;  t <= Nt;  t++ )  {                               
			                                                      // x loop
      for ( ix=1;  ix  <  Nx-1;  ix++ ) T[ix][1] = T[ix][0]      
                      + cons*(T[ix + 1][0] + T[ix-1][0]-2.*T[ix][0]);
      if ( t%10==0 || t==1 )  {                 // Save every N steps
        for ( ix = 0; ix<Nx;  ix++ ) q.println(T[ix][1]); 
        q.println();                           // Blank line ends row
      } 
      for ( ix = 1; ix<Nx-1; ix++ ) T[ix][0]=T[ix][1];  // New to old
    }                                                   // End t loop
    System.out.println("data stored in EqHeat.dat"); 
  }                                                       // End main
}                                                        // End class