Actual source code: dgefa7.c
1: /*$Id: dgefa7.c,v 1.10 2001/04/07 15:51:54 bsmith Exp $*/
2: /*
3: Inverts 7 by 7 matrix using partial pivoting.
5: Used by the sparse factorization routines in
6: src/mat/impls/baij/seq and src/mat/impls/bdiag/seq
8: See also src/inline/ilu.h
10: This is a combination of the Linpack routines
11: dgefa() and dgedi() specialized for a size of 7.
13: */
14: #include petsc.h
16: int Kernel_A_gets_inverse_A_7(MatScalar *a)
17: {
18: int i__2,i__3,kp1,j,k,l,ll,i,ipvt[7],kb,k3;
19: int k4,j3;
20: MatScalar *aa,*ax,*ay,work[49],stmp;
21: MatReal tmp,max;
23: /* gaussian elimination with partial pivoting */
26: /* Parameter adjustments */
27: a -= 8;
29: for (k = 1; k <= 6; ++k) {
30: kp1 = k + 1;
31: k3 = 7*k;
32: k4 = k3 + k;
33: /* find l = pivot index */
35: i__2 = 7 - k;
36: aa = &a[k4];
37: max = PetscAbsScalar(aa[0]);
38: l = 1;
39: for (ll=1; ll<i__2; ll++) {
40: tmp = PetscAbsScalar(aa[ll]);
41: if (tmp > max) { max = tmp; l = ll+1;}
42: }
43: l += k - 1;
44: ipvt[k-1] = l;
46: if (a[l + k3] == 0.) {
47: SETERRQ(k,"Zero pivot");
48: }
50: /* interchange if necessary */
52: if (l != k) {
53: stmp = a[l + k3];
54: a[l + k3] = a[k4];
55: a[k4] = stmp;
56: }
58: /* compute multipliers */
60: stmp = -1. / a[k4];
61: i__2 = 7 - k;
62: aa = &a[1 + k4];
63: for (ll=0; ll<i__2; ll++) {
64: aa[ll] *= stmp;
65: }
67: /* row elimination with column indexing */
69: ax = &a[k4+1];
70: for (j = kp1; j <= 7; ++j) {
71: j3 = 7*j;
72: stmp = a[l + j3];
73: if (l != k) {
74: a[l + j3] = a[k + j3];
75: a[k + j3] = stmp;
76: }
78: i__3 = 7 - k;
79: ay = &a[1+k+j3];
80: for (ll=0; ll<i__3; ll++) {
81: ay[ll] += stmp*ax[ll];
82: }
83: }
84: }
85: ipvt[6] = 7;
86: if (a[56] == 0.) {
87: SETERRQ(3,"Zero pivot,final row");
88: }
90: /*
91: Now form the inverse
92: */
94: /* compute inverse(u) */
96: for (k = 1; k <= 7; ++k) {
97: k3 = 7*k;
98: k4 = k3 + k;
99: a[k4] = 1.0 / a[k4];
100: stmp = -a[k4];
101: i__2 = k - 1;
102: aa = &a[k3 + 1];
103: for (ll=0; ll<i__2; ll++) aa[ll] *= stmp;
104: kp1 = k + 1;
105: if (7 < kp1) continue;
106: ax = aa;
107: for (j = kp1; j <= 7; ++j) {
108: j3 = 7*j;
109: stmp = a[k + j3];
110: a[k + j3] = 0.0;
111: ay = &a[j3 + 1];
112: for (ll=0; ll<k; ll++) {
113: ay[ll] += stmp*ax[ll];
114: }
115: }
116: }
118: /* form inverse(u)*inverse(l) */
120: for (kb = 1; kb <= 6; ++kb) {
121: k = 7 - kb;
122: k3 = 7*k;
123: kp1 = k + 1;
124: aa = a + k3;
125: for (i = kp1; i <= 7; ++i) {
126: work[i-1] = aa[i];
127: aa[i] = 0.0;
128: }
129: for (j = kp1; j <= 7; ++j) {
130: stmp = work[j-1];
131: ax = &a[7*j + 1];
132: ay = &a[k3 + 1];
133: ay[0] += stmp*ax[0];
134: ay[1] += stmp*ax[1];
135: ay[2] += stmp*ax[2];
136: ay[3] += stmp*ax[3];
137: ay[4] += stmp*ax[4];
138: ay[5] += stmp*ax[5];
139: ay[6] += stmp*ax[6];
140: }
141: l = ipvt[k-1];
142: if (l != k) {
143: ax = &a[k3 + 1];
144: ay = &a[7*l + 1];
145: stmp = ax[0]; ax[0] = ay[0]; ay[0] = stmp;
146: stmp = ax[1]; ax[1] = ay[1]; ay[1] = stmp;
147: stmp = ax[2]; ax[2] = ay[2]; ay[2] = stmp;
148: stmp = ax[3]; ax[3] = ay[3]; ay[3] = stmp;
149: stmp = ax[4]; ax[4] = ay[4]; ay[4] = stmp;
150: stmp = ax[5]; ax[5] = ay[5]; ay[5] = stmp;
151: stmp = ax[6]; ax[6] = ay[6]; ay[6] = stmp;
152: }
153: }
154: return(0);
155: }