Actual source code: dgedi.c
petsc-3.13.6 2020-09-29
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      2: /*
      3:               This file creating by running f2c
      4:             linpack. this version dated 08/14/78
      5:       cleve moler, university of new mexico, argonne national lab.

      7:       Computes the inverse of a matrix given its factors and pivots
      8:     calculated by PetscLINPACKgefa(). Performed in-place for an n by n
      9:     dense matrix.

     11:        Used by the sparse factorization routines in
     12:      src/mat/impls/baij/seq

     14: */

     16:  #include <petscsys.h>
     17:  #include <petsc/private/kernels/blockinvert.h>

     19: PETSC_INTERN PetscErrorCode PetscLINPACKgedi(MatScalar *a,PetscInt n,PetscInt *ipvt,MatScalar *work)
     20: {
     21:   PetscInt  i__2,kb,kp1,nm1,i,j,k,l,ll,kn,knp1,jn1;
     22:   MatScalar *aa,*ax,*ay,tmp;
     23:   MatScalar t;

     26:   --work;
     27:   --ipvt;
     28:   a -= n + 1;

     30:   /*     compute inverse(u) */

     32:   for (k = 1; k <= n; ++k) {
     33:     kn      = k*n;
     34:     knp1    = kn + k;
     35:     a[knp1] = 1.0 / a[knp1];
     36:     t       = -a[knp1];
     37:     i__2    = k - 1;
     38:     aa      = &a[1 + kn];
     39:     for (ll=0; ll<i__2; ll++) aa[ll] *= t;
     40:     kp1 = k + 1;
     41:     if (n < kp1) continue;
     42:     ax = aa;
     43:     for (j = kp1; j <= n; ++j) {
     44:       jn1        = j*n;
     45:       t          = a[k + jn1];
     46:       a[k + jn1] = 0.;
     47:       ay         = &a[1 + jn1];
     48:       for (ll=0; ll<k; ll++) ay[ll] += t*ax[ll];
     49:     }
     50:   }

     52:   /*    form inverse(u)*inverse(l) */

     54:   nm1 = n - 1;
     55:   if (nm1 < 1) {
     56:       return(0);
     57:   }
     58:   for (kb = 1; kb <= nm1; ++kb) {
     59:     k   = n - kb;
     60:     kn  = k*n;
     61:     kp1 = k + 1;
     62:     aa  = a + kn;
     63:     for (i = kp1; i <= n; ++i) {
     64:       work[i] = aa[i];
     65:       aa[i]   = 0.;
     66:     }
     67:     for (j = kp1; j <= n; ++j) {
     68:       t  = work[j];
     69:       ax = &a[j * n + 1];
     70:       ay = &a[kn + 1];
     71:       for (ll=0; ll<n; ll++) ay[ll] += t*ax[ll];
     72:     }
     73:     l = ipvt[k];
     74:     if (l != k) {
     75:       ax = &a[kn + 1];
     76:       ay = &a[l * n + 1];
     77:       for (ll=0; ll<n; ll++) {
     78:         tmp    = ax[ll];
     79:         ax[ll] = ay[ll];
     80:         ay[ll] = tmp;
     81:       }
     82:     }
     83:   }
     84:   return(0);
     85: }