1a5eb4965SSatish Balay #ifdef PETSC_RCS_HEADER 2*9d8b60e5SBarry Smith static char vcid[] = "$Id: dgefa.c,v 1.12 1998/12/24 02:54:37 bsmith 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. 859539b86SBarry Smith 959539b86SBarry Smith Does an LU factorization with partial pivoting of a dense 10*9d8b60e5SBarry Smith n by n matrix. 11*9d8b60e5SBarry Smith 12*9d8b60e5SBarry Smith Used by the sparse factorization routines in 1359539b86SBarry Smith src/mat/impls/baij/seq and src/mat/impls/bdiag/seq 1459539b86SBarry Smith 159fd41dd0SBarry Smith */ 169fd41dd0SBarry Smith #include "petsc.h" 179fd41dd0SBarry Smith 185615d1e5SSatish Balay #undef __FUNC__ 195615d1e5SSatish Balay #define __FUNC__ "Linpack_DGEFA" 203f1db9ecSBarry Smith int Linpack_DGEFA(MatScalar *a, int n, int *ipvt) 219fd41dd0SBarry Smith { 228d3e6ddaSBarry Smith int i__2, i__3, kp1, nm1, j, k, l,ll,kn,knp1,jn1; 233f1db9ecSBarry Smith MatScalar t,*ax,*ay,*aa; 243f1db9ecSBarry Smith MatFloat tmp,max; 259fd41dd0SBarry Smith 269fd41dd0SBarry Smith /* gaussian elimination with partial pivoting */ 279fd41dd0SBarry Smith 283a40ed3dSBarry Smith PetscFunctionBegin; 299fd41dd0SBarry Smith /* Parameter adjustments */ 309fd41dd0SBarry Smith --ipvt; 3139d66777SBarry Smith a -= n + 1; 329fd41dd0SBarry Smith 339fd41dd0SBarry Smith /* Function Body */ 349fd41dd0SBarry Smith nm1 = n - 1; 3539d66777SBarry Smith for (k = 1; k <= nm1; ++k) { 369fd41dd0SBarry Smith kp1 = k + 1; 3739d66777SBarry Smith kn = k*n; 3839d66777SBarry Smith knp1 = k*n + k; 399fd41dd0SBarry Smith 409fd41dd0SBarry Smith /* find l = pivot index */ 419fd41dd0SBarry Smith 429fd41dd0SBarry Smith i__2 = n - k + 1; 4339d66777SBarry Smith aa = &a[knp1]; 449fd41dd0SBarry Smith max = PetscAbsScalar(aa[0]); 459fd41dd0SBarry Smith l = 1; 469fd41dd0SBarry Smith for ( ll=1; ll<i__2; ll++ ) { 479fd41dd0SBarry Smith tmp = PetscAbsScalar(aa[ll]); 489fd41dd0SBarry Smith if (tmp > max) { max = tmp; l = ll+1;} 499fd41dd0SBarry Smith } 509fd41dd0SBarry Smith l += k - 1; 519fd41dd0SBarry Smith ipvt[k] = l; 529fd41dd0SBarry Smith 5339d66777SBarry Smith if (a[l + kn] == 0.) { 54e3372554SBarry Smith SETERRQ(k,0,"Zero pivot"); 559fd41dd0SBarry Smith } 569fd41dd0SBarry Smith 579fd41dd0SBarry Smith /* interchange if necessary */ 589fd41dd0SBarry Smith 599fd41dd0SBarry Smith if (l != k) { 6039d66777SBarry Smith t = a[l + kn]; 6139d66777SBarry Smith a[l + kn] = a[knp1]; 6239d66777SBarry Smith a[knp1] = t; 639fd41dd0SBarry Smith } 649fd41dd0SBarry Smith 659fd41dd0SBarry Smith /* compute multipliers */ 669fd41dd0SBarry Smith 6739d66777SBarry Smith t = -1. / a[knp1]; 689fd41dd0SBarry Smith i__2 = n - k; 6939d66777SBarry Smith aa = &a[1 + knp1]; 709fd41dd0SBarry Smith for ( ll=0; ll<i__2; ll++ ) { 719fd41dd0SBarry Smith aa[ll] *= t; 729fd41dd0SBarry Smith } 739fd41dd0SBarry Smith 749fd41dd0SBarry Smith /* row elimination with column indexing */ 759fd41dd0SBarry Smith 7639d66777SBarry Smith ax = aa; 779fd41dd0SBarry Smith for (j = kp1; j <= n; ++j) { 788d3e6ddaSBarry Smith jn1 = j*n; 798d3e6ddaSBarry Smith t = a[l + jn1]; 809fd41dd0SBarry Smith if (l != k) { 818d3e6ddaSBarry Smith a[l + jn1] = a[k + jn1]; 828d3e6ddaSBarry Smith a[k + jn1] = t; 839fd41dd0SBarry Smith } 849fd41dd0SBarry Smith 859fd41dd0SBarry Smith i__3 = n - k; 868d3e6ddaSBarry Smith ay = &a[1+k+jn1]; 879fd41dd0SBarry Smith for ( ll=0; ll<i__3; ll++ ) { 889fd41dd0SBarry Smith ay[ll] += t*ax[ll]; 899fd41dd0SBarry Smith } 909fd41dd0SBarry Smith } 919fd41dd0SBarry Smith } 929fd41dd0SBarry Smith ipvt[n] = n; 939fd41dd0SBarry Smith if (a[n + n * n] == 0.) { 94e3372554SBarry Smith SETERRQ(n,0,"Zero pivot,final row"); 959fd41dd0SBarry Smith } 963a40ed3dSBarry Smith PetscFunctionReturn(0); 979fd41dd0SBarry Smith } 989fd41dd0SBarry Smith 99