/* tr2.f -- translated by f2c cc*/
/*fev 98  slop val*/ 

/* vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv */
/* Subroutine */
/* void tridiag3fr_ */

import java.util.*;
import java.awt.*;
import java.applet.Applet;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;

 
 
 
class tridiago    
 {
   static double diagi[];
   static double diagp[];
   static double diags[];
   static double rhs[];
   static double u[];
   static double uo[];
   static double a[];
   static double b[];
   static int n;
   static double dy;
   static double dt;
   static double u0;
   static double un;
   static double q;
   static double Bi;
   static boolean slope=false;
   static boolean mixte=false;
   static boolean val  =false;
   static boolean sym  =false;


 
  public static void prems()
 { 
   System.out.println(" initialize tridiago "); 
   diagi = new double[n+1];
   diagp = new double[n+1];
   diags = new double[n+1];
   rhs   = new double[n+1]; 
   u     = new double[n+1];
   uo    = new double[n+1];  
   a     = new double[n+1];
   b     = new double[n+1];
   }

 public static void inverse()
 { int j;
   double aa,bb,cc,dd;
   double qn=0;
/*     inversion de matrice tridiago                              */
/*     ai ui-1 + bi ui +ci ui+1 = rhs i                          */
/*     diagi[j] u[j-1] +  diagp[j] u[j] + diags[j] u[j+1]= rhs[j]*/
/*    	u[j] = a[j] * u[j + 1] + b[j];                            */
/*     14 nov 90 -  23 nov 92 -  aout 95 - 8 mars 96 Aout 05  */
/*     Peyret Taylor p 20 */
/*     l indice varie de 0 a N */

   for (j=0; j<=n;j++)
   {
   /*     a u"  +  b u' + c u    =  d                                             */ 
/********************************************************************/
		  aa = 1; 
          bb = 0;				                       
		  cc =  - (1./dt); 
		  dd =  -(uo[j])/dt;         
		  
	 diags[j] =   1.*aa  + bb/2 * (dy);
	 diagp[j] =  -2.*aa         + cc * (dy) * (dy);
	 diagi[j] =   1.*aa  - bb/2 * (dy);
	 rhs[j] =           dd * (dy) * (dy);
		}
    j = 0;
    /*a[0] = 0.f;  b[0] = *u0;  donne'e de u0*/
    /*a[0] = 1.f;  b[0] = 0; modif du/dy=0 en 0*/
    /*a[0] = 1.f;  b[0] = dy;du/dy=1 en 0*/
     
  if(slope){
   a[0] = 1.;  b[0] = (q)*dy;
   }
  if(val){
   a[0] = 0.;  b[0] = u0; }
  if(mixte){  double Te=0;
   a[0]= (Bi/dy)/(1+Bi/dy); b[0] = Te/(1+Bi/dy);}
 
    for (j = 1; j < n; ++j) {
	dd = 1./(diagp[j] + diagi[j] * a[j - 1]);
	a[j] = -diags[j] * dd ;
	b[j] = (rhs[j] - diagi[j] * b[j - 1]) * dd ;
    }

if(sym)
    {
	 u[n-1] = (rhs[n-1]- b[n-2]*diagi[n-1] - diags[n-1]*qn*dy)/(diagp[n-1] + diagi[n-1] * a[n - 2] + diags[n-1]);
	 u[n] = u[n-1] + qn*dy;
	 for (j = n - 2; j >= 0; --j) {   
	u[j] = a[j] * u[j + 1] + b[j];
    }
	}
else
	{
	u[n] = un;
    for (j = n - 1; j >= 0; --j) {   
	u[j] = a[j] * u[j + 1] + b[j];
    }
    }
} /* tridiago2_ */

}
//http://www.seismo.unr.edu/ftp/pub/louie/class/757/java/imhf.java