411 REFERENCE · Wikibooks
Linear Algebra and the C Language/a01t
Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.
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/* Save as : vgj1piv.h */
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double pivotbest_gj1Ab_mR(
double **Ab,
int pv
)
{
double pvbest = fabs(Ab[pv][pv]);
int best_r = pv;
int best_c = pv;
int r;
int c;
for ( r=pv; r<Ab[R_SIZE][C0]; r++)
for ( c=pv; c<Ab[R_SIZE][C0]; c++)
if(fabs(Ab[r][c])>pvbest)
{
pvbest = fabs(Ab[r][c]);
best_r = r;
best_c = c;
}
if(best_r!=pv) swapR_mR(Ab,pv,best_r);
if(best_c!=pv) swapC_withR0_mR(Ab,pv,best_c);
return(pvbest);
}
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double **zero_under_pivot_gj1Ab_mR(
double **Ab,
int pv
)
{
double pivot = Ab[pv][pv];
int r;
if(fabs(pivot)>ERROR_E)
{
mulR_mR( Ab,(1./pivot),pv);
for( r=(pv+C1); r<Ab[R_SIZE][C0]; r++)
addR_mR( Ab,(-Ab[r][pv]),pv,r);
}
return(Ab);
}
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double **zero_above_pivot_gj1Ab_mR(
double **Ab,
int pv
)
{
int r;
if(fabs(Ab[pv][pv])>ERROR_E)
for( r=(pv-R1); r>=R1; r--)
addR_mR( Ab,(-Ab[r][pv]),pv,r);
return(Ab);
}
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