1*29bbc08cSBarry Smith /*$Id: dgefa.c,v 1.19 2000/04/12 04:23:32 bsmith Exp bsmith $*/ 29fd41dd0SBarry Smith /* 39fd41dd0SBarry Smith This routine was converted by f2c from Linpack source 49fd41dd0SBarry Smith linpack. this version dated 08/14/78 59fd41dd0SBarry Smith cleve moler, university of new mexico, argonne national lab. 659539b86SBarry Smith 759539b86SBarry Smith Does an LU factorization with partial pivoting of a dense 89d8b60e5SBarry Smith n by n matrix. 99d8b60e5SBarry Smith 109d8b60e5SBarry Smith Used by the sparse factorization routines in 1159539b86SBarry Smith src/mat/impls/baij/seq and src/mat/impls/bdiag/seq 1259539b86SBarry Smith 1371c5468dSBarry Smith See also src/inline/ilu.h 149fd41dd0SBarry Smith */ 159fd41dd0SBarry Smith #include "petsc.h" 169fd41dd0SBarry Smith 175615d1e5SSatish Balay #undef __FUNC__ 18b2863d3aSBarry Smith #define __FUNC__ /*<a name=""></a>*/"LINPACKdgefa" 19596552b5SBarry Smith int LINPACKdgefa(MatScalar *a,int n,int *ipvt) 209fd41dd0SBarry Smith { 218d3e6ddaSBarry Smith int i__2,i__3,kp1,nm1,j,k,l,ll,kn,knp1,jn1; 223f1db9ecSBarry Smith MatScalar t,*ax,*ay,*aa; 23329f5518SBarry Smith MatReal tmp,max; 249fd41dd0SBarry Smith 259fd41dd0SBarry Smith /* gaussian elimination with partial pivoting */ 269fd41dd0SBarry Smith 273a40ed3dSBarry Smith PetscFunctionBegin; 289fd41dd0SBarry Smith /* Parameter adjustments */ 299fd41dd0SBarry Smith --ipvt; 3039d66777SBarry Smith a -= n + 1; 319fd41dd0SBarry Smith 329fd41dd0SBarry Smith /* Function Body */ 339fd41dd0SBarry Smith nm1 = n - 1; 3439d66777SBarry Smith for (k = 1; k <= nm1; ++k) { 359fd41dd0SBarry Smith kp1 = k + 1; 3639d66777SBarry Smith kn = k*n; 3739d66777SBarry Smith knp1 = k*n + k; 389fd41dd0SBarry Smith 399fd41dd0SBarry Smith /* find l = pivot index */ 409fd41dd0SBarry Smith 419fd41dd0SBarry Smith i__2 = n - k + 1; 4239d66777SBarry Smith aa = &a[knp1]; 439fd41dd0SBarry Smith max = PetscAbsScalar(aa[0]); 449fd41dd0SBarry Smith l = 1; 459fd41dd0SBarry Smith for (ll=1; ll<i__2; ll++) { 469fd41dd0SBarry Smith tmp = PetscAbsScalar(aa[ll]); 479fd41dd0SBarry Smith if (tmp > max) { max = tmp; l = ll+1;} 489fd41dd0SBarry Smith } 499fd41dd0SBarry Smith l += k - 1; 509fd41dd0SBarry Smith ipvt[k] = l; 519fd41dd0SBarry Smith 5239d66777SBarry Smith if (a[l + kn] == 0.) { 53*29bbc08cSBarry Smith SETERRQ(k,"Zero pivot"); 549fd41dd0SBarry Smith } 559fd41dd0SBarry Smith 569fd41dd0SBarry Smith /* interchange if necessary */ 579fd41dd0SBarry Smith 589fd41dd0SBarry Smith if (l != k) { 5939d66777SBarry Smith t = a[l + kn]; 6039d66777SBarry Smith a[l + kn] = a[knp1]; 6139d66777SBarry Smith a[knp1] = t; 629fd41dd0SBarry Smith } 639fd41dd0SBarry Smith 649fd41dd0SBarry Smith /* compute multipliers */ 659fd41dd0SBarry Smith 6639d66777SBarry Smith t = -1. / a[knp1]; 679fd41dd0SBarry Smith i__2 = n - k; 6839d66777SBarry Smith aa = &a[1 + knp1]; 699fd41dd0SBarry Smith for (ll=0; ll<i__2; ll++) { 709fd41dd0SBarry Smith aa[ll] *= t; 719fd41dd0SBarry Smith } 729fd41dd0SBarry Smith 739fd41dd0SBarry Smith /* row elimination with column indexing */ 749fd41dd0SBarry Smith 7539d66777SBarry Smith ax = aa; 769fd41dd0SBarry Smith for (j = kp1; j <= n; ++j) { 778d3e6ddaSBarry Smith jn1 = j*n; 788d3e6ddaSBarry Smith t = a[l + jn1]; 799fd41dd0SBarry Smith if (l != k) { 808d3e6ddaSBarry Smith a[l + jn1] = a[k + jn1]; 818d3e6ddaSBarry Smith a[k + jn1] = t; 829fd41dd0SBarry Smith } 839fd41dd0SBarry Smith 849fd41dd0SBarry Smith i__3 = n - k; 858d3e6ddaSBarry Smith ay = &a[1+k+jn1]; 869fd41dd0SBarry Smith for (ll=0; ll<i__3; ll++) { 879fd41dd0SBarry Smith ay[ll] += t*ax[ll]; 889fd41dd0SBarry Smith } 899fd41dd0SBarry Smith } 909fd41dd0SBarry Smith } 919fd41dd0SBarry Smith ipvt[n] = n; 929fd41dd0SBarry Smith if (a[n + n * n] == 0.) { 93*29bbc08cSBarry Smith SETERRQ(n,"Zero pivot,final row"); 949fd41dd0SBarry Smith } 953a40ed3dSBarry Smith PetscFunctionReturn(0); 969fd41dd0SBarry Smith } 979fd41dd0SBarry Smith 98