411 REFERENCE · Wikibooks
Linear Algebra and the C Language/a02r
Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.
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/* Save as : vgj2piv.h */
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double pivotbest_gj2Ab_mR(
double **Ab,
int pivot_r,
int pivot_c
)
{
double pivotbest = fabs(Ab[pivot_r][pivot_c]);
int best_r = pivot_r;
int best_c = pivot_c;
int r;
int c;
for ( r=pivot_r; r<Ab[R_SIZE ][C0]; r++)
for ( c=pivot_c; c<Ab[C_SIZE_A][C0]; c++)
if(fabs(Ab[r][c])>pivotbest)
{
pivotbest = fabs(Ab[r][c]);
best_r = r;
best_c = c;
}
if(best_r!=pivot_r) swapR_mR(Ab,pivot_r,best_r);
if(best_c!=pivot_c) swapC_withR0_mR(Ab,pivot_c,best_c);
return(pivotbest);
}
/* ------------------------------------ */
void zero_under_pivot_gj2Ab_mR(
double **Ab,
int pivot_r,
int pivot_c
)
{
double pivot = Ab[pivot_r][pivot_c];
int r;
if(fabs(pivot)>ERROR_E)
{
mulR_mR( Ab,(1./pivot),pivot_r);
for( r=(pivot_r+C1); r<Ab[R_SIZE][C0]; r++)
addR_mR( Ab,(-Ab[r][pivot_c]),pivot_r,r);
}
}
/* ------------------------------------ */
double **zero_above_pivot_gj2Ab_mR(
double **Ab,
int pivot_r,
int pivot_c
)
{
int r;
if(fabs(Ab[pivot_r][pivot_c])>ERROR_E)
for( r=(pivot_r-C1); r>=R1; r--)
addR_mR( Ab,(-Ab[r][pivot_c]),pivot_r,r);
return(Ab);
}
/* ------------------------------------ */
/* ------------------------------------ */
void zero4_under_all_pivot_mR(
double **Ab
)
{
int r= R1;
int c= C1;
while((r<Ab[R_SIZE][C0]) &&
(c<Ab[C_SIZE_A][C0])
)
{
if(fabs(pivotbest_gj2Ab_mR(Ab,r,r))>ERROR_E)
zero_under_pivot_gj2Ab_mR(Ab,r,r);
r++;
}
}
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