Cutting the residual calculation

Instead of calculating residual for the next iteration, we calculate residual
iteration. This is an acceptable deviation, and a significant optimization.
Signed-off-by: Gaurav Kukreja <mailme.gaurav@gmail.com>

heat-seq/heat.h

@@ -57,8 +57,10 @@ void relax_gauss( double *u,
 		  unsigned sizex, unsigned sizey  );
 
 // Jacobi: relax_jacobi.c
+#if 0
 double residual_jacobi( double *u,
 			unsigned sizex, unsigned sizey );
+#endif
 double relax_jacobi_return_residual( double *u, double *utmp,
 		   unsigned sizex, unsigned sizey ); 
 

heat-seq/relax_jacobi.c

@@ -7,6 +7,7 @@
 
 #include "heat.h"
 
+#if 0
 /*
  * Residual (length of error vector)
  * between current solution and next after a Jacobi step
@@ -33,7 +34,7 @@ double residual_jacobi( double *u,
 
     return sum;
 }
-
+#endif
 
 /*
  * One Jacobi iteration step
@@ -44,27 +45,17 @@ double relax_jacobi_return_residual( double *u, double *utmp,
 	int i, j;
 	double unew, diff, sum=0.0;
 
-	for( i=1; i<sizey; i++ )
+	for( i=1; i<sizey-1; i++ )
 	{
 		for( j=1; j<sizex-1; j++ )
 		{
-			if(i<sizey-1)
 			{
 				utmp[i*sizex + j]= 0.25 * (u[ i*sizex+j -1 ]+  // left
 						u[ i*sizex+j +1 ]+  // right
 						u[ (i-1)*sizex + j ]+  // top
 						u[ (i+1)*sizex + j ]); // bottom
-			}
-
-			//Residual Calculation
-			if(i>1)
-			{
-				unew = 0.25 * (utmp[ (i-1)*sizex+j -1 ]+  // left
-						utmp[ (i-1)*sizex+j +1 ]+  // right
-						utmp[ (i-2)*sizex + j ]+  // top
-						utmp[ (i)*sizex + j ]); // bottom
 
-				diff = unew - utmp[(i-1)*sizex+j];
+				diff = utmp[i*sizex + j] - u[i*sizex +j];
 				sum += diff * diff;
 			}
 		}