1a5eb4965SSatish Balay #ifdef PETSC_RCS_HEADER 2*3a40ed3dSBarry Smith static char vcid[] = "$Id: dgefa.c,v 1.8 1997/07/09 20:55:07 balay Exp bsmith $"; 34431cf12SSatish Balay #endif 49fd41dd0SBarry Smith /* 59fd41dd0SBarry Smith This routine was converted by f2c from Linpack source 69fd41dd0SBarry Smith linpack. this version dated 08/14/78 79fd41dd0SBarry Smith cleve moler, university of new mexico, argonne national lab. 89fd41dd0SBarry Smith */ 99fd41dd0SBarry Smith #include "petsc.h" 109fd41dd0SBarry Smith 115615d1e5SSatish Balay #undef __FUNC__ 125615d1e5SSatish Balay #define __FUNC__ "Linpack_DGEFA" 139fd41dd0SBarry Smith int Linpack_DGEFA(Scalar *a, int n, int *ipvt) 149fd41dd0SBarry Smith { 1539d66777SBarry Smith int i__2, i__3, kp1, nm1, j, k, l,ll,kn,knp1,jn; 166d84be18SBarry Smith Scalar t,*aa,*ax,*ay; 176d84be18SBarry Smith double tmp,max; 189fd41dd0SBarry Smith 199fd41dd0SBarry Smith /* gaussian elimination with partial pivoting */ 209fd41dd0SBarry Smith 21*3a40ed3dSBarry Smith PetscFunctionBegin; 229fd41dd0SBarry Smith /* Parameter adjustments */ 239fd41dd0SBarry Smith --ipvt; 2439d66777SBarry Smith a -= n + 1; 259fd41dd0SBarry Smith 269fd41dd0SBarry Smith /* Function Body */ 279fd41dd0SBarry Smith nm1 = n - 1; 2839d66777SBarry Smith for (k = 1; k <= nm1; ++k) { 299fd41dd0SBarry Smith kp1 = k + 1; 3039d66777SBarry Smith kn = k*n; 3139d66777SBarry Smith knp1 = k*n + k; 329fd41dd0SBarry Smith 339fd41dd0SBarry Smith /* find l = pivot index */ 349fd41dd0SBarry Smith 359fd41dd0SBarry Smith i__2 = n - k + 1; 3639d66777SBarry Smith aa = &a[knp1]; 379fd41dd0SBarry Smith max = PetscAbsScalar(aa[0]); 389fd41dd0SBarry Smith l = 1; 399fd41dd0SBarry Smith for ( ll=1; ll<i__2; ll++ ) { 409fd41dd0SBarry Smith tmp = PetscAbsScalar(aa[ll]); 419fd41dd0SBarry Smith if (tmp > max) { max = tmp; l = ll+1;} 429fd41dd0SBarry Smith } 439fd41dd0SBarry Smith l += k - 1; 449fd41dd0SBarry Smith ipvt[k] = l; 459fd41dd0SBarry Smith 4639d66777SBarry Smith if (a[l + kn] == 0.) { 47e3372554SBarry Smith SETERRQ(k,0,"Zero pivot"); 489fd41dd0SBarry Smith } 499fd41dd0SBarry Smith 509fd41dd0SBarry Smith /* interchange if necessary */ 519fd41dd0SBarry Smith 529fd41dd0SBarry Smith if (l != k) { 5339d66777SBarry Smith t = a[l + kn]; 5439d66777SBarry Smith a[l + kn] = a[knp1]; 5539d66777SBarry Smith a[knp1] = t; 569fd41dd0SBarry Smith } 579fd41dd0SBarry Smith 589fd41dd0SBarry Smith /* compute multipliers */ 599fd41dd0SBarry Smith 6039d66777SBarry Smith t = -1. / a[knp1]; 619fd41dd0SBarry Smith i__2 = n - k; 6239d66777SBarry Smith aa = &a[1 + knp1]; 639fd41dd0SBarry Smith for ( ll=0; ll<i__2; ll++ ) { 649fd41dd0SBarry Smith aa[ll] *= t; 659fd41dd0SBarry Smith } 669fd41dd0SBarry Smith 679fd41dd0SBarry Smith /* row elimination with column indexing */ 689fd41dd0SBarry Smith 6939d66777SBarry Smith ax = aa; 709fd41dd0SBarry Smith for (j = kp1; j <= n; ++j) { 7139d66777SBarry Smith jn = j*n; 7239d66777SBarry Smith t = a[l + jn]; 739fd41dd0SBarry Smith if (l != k) { 7439d66777SBarry Smith a[l + jn] = a[k + jn]; 7539d66777SBarry Smith a[k + jn] = t; 769fd41dd0SBarry Smith } 779fd41dd0SBarry Smith 789fd41dd0SBarry Smith i__3 = n - k; 7939d66777SBarry Smith ay = &a[1+k+jn]; 809fd41dd0SBarry Smith for ( ll=0; ll<i__3; ll++ ) { 819fd41dd0SBarry Smith ay[ll] += t*ax[ll]; 829fd41dd0SBarry Smith } 839fd41dd0SBarry Smith } 849fd41dd0SBarry Smith } 859fd41dd0SBarry Smith ipvt[n] = n; 869fd41dd0SBarry Smith if (a[n + n * n] == 0.) { 87e3372554SBarry Smith SETERRQ(n,0,"Zero pivot,final row"); 889fd41dd0SBarry Smith } 89*3a40ed3dSBarry Smith PetscFunctionReturn(0); 909fd41dd0SBarry Smith } 919fd41dd0SBarry Smith 92