/* 
*********************************************************}
* Tune.java: a matrix algebra program to be tuned for performace         
c                                                                     
c  converted from tune.f in "Computational Physics" by Landau and Paez 
c              mod to start indices at 0 not 1           
c                                                                     
c  written by: Paul J Fink and Rubin Landau                         
c              code copyrighted by RH Landau                       
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*/ 
public class Tune_Slow
 {
    public static void main(String[] argv) 
    { 
      final int Ldim = 100;
      int i, j, iter = 0;
      double [][] ham = new double [Ldim] [Ldim];
      double [] coef  = new double [Ldim];
      double [] sigma = new double [Ldim];  
      double err, ener, ovlp, step=0.,time, dummy=2.;

      // Store initial time  
      time = System.currentTimeMillis();
	  //   
	  //       set up Hamiltonian & starting vector 
	  for ( i = 0; i <= Ldim-1; i++)
	      {
		  for ( j=0; j <= Ldim-1; j++)
		      {
			  if (Math.abs(j-i) >10) {ham[j][i] = 0.0;} 
			  else  ham[j][i] = Math.pow(0.3, Math.abs(j-i));   
		      }   
		  ham[i][i] = i+1 ;      // Diagnol H elements
		  coef[i] = 0.0  ;       //Eigenvector elements
	      } 
     // 
     //      start iterating towards the solution   	  
	  coef[1] = 1.0  ;   // Guess 1st eigenvector = 1, 0, ...0
	  err = 1.0  ;       // Arbitrary err to begin 	
         System.out.println ("Iteration #\tEnergy\t\tERR\t\tTotal Time "); 

     // iterate until converge or 15 tries
     while (iter <15 && err > 1.0e-6)
	 {iter = iter + 1  ;
     //
     //       compute current energy \& norm, \& normalize     
	 ener = 0.0   ;
	 ovlp = 0.0  ; 
	 for ( i= 0; i <= Ldim-1; i++) // outter loop
	  {   
	      ovlp = ovlp + coef[i]*coef[i] ;  
	      sigma[i] = 0.0;   
	      for ( j= 0; j <= Ldim-1; j++)  // inner loop
		  {
		      sigma[i] = sigma[i] + coef[j]*ham[j][i];}
	              ener = ener + coef[i]*sigma[i] ;
		      for ( int k= 0; k <= Ldim*Ldim; k++)  // do nothing loop
			  {dummy = Math.pow(k,Math.pow(1,j));}
	          }  
      ener = ener/ovlp  ;
      for (  i = 1; i<= Ldim-1; i++)  //Normalize, this starts at 1
	 {   
         coef[i] = coef[i]/Math.sqrt(ovlp) ;  
         sigma[i] = sigma[i]/Math.sqrt(ovlp) ;  
	  }    
     //     compute update and error     
     //   
      err = 0.0  ;  
      for ( i = 2; i <= Ldim-1; i++)
	  {  
         step = (sigma[i] - ener*coef[i])/(ener-ham[i][i])   ; 
         coef[i] = coef[i] + step    ;
         err = err + Math.pow(step,2)    ;
	  }  
      err = Math.sqrt(err)   ; 
       System.out.println ("\t#"+iter+"\t"+ener+ "\t" +err+ "\t"+(System.currentTimeMillis() -time)/1000);
      }     
     // output elapsed time
     time = (System.currentTimeMillis() - time)/1000;
     System.out.println("time= "+ time + "s");
}
 }