Annotation of rpl/lapack/lapack/zgesv.f, revision 1.3
1.1 bertrand 1: SUBROUTINE ZGESV( N, NRHS, A, LDA, IPIV, B, LDB, INFO )
2: *
3: * -- LAPACK driver routine (version 3.2) --
4: * -- LAPACK is a software package provided by Univ. of Tennessee, --
5: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
6: * November 2006
7: *
8: * .. Scalar Arguments ..
9: INTEGER INFO, LDA, LDB, N, NRHS
10: * ..
11: * .. Array Arguments ..
12: INTEGER IPIV( * )
13: COMPLEX*16 A( LDA, * ), B( LDB, * )
14: * ..
15: *
16: * Purpose
17: * =======
18: *
19: * ZGESV computes the solution to a complex system of linear equations
20: * A * X = B,
21: * where A is an N-by-N matrix and X and B are N-by-NRHS matrices.
22: *
23: * The LU decomposition with partial pivoting and row interchanges is
24: * used to factor A as
25: * A = P * L * U,
26: * where P is a permutation matrix, L is unit lower triangular, and U is
27: * upper triangular. The factored form of A is then used to solve the
28: * system of equations A * X = B.
29: *
30: * Arguments
31: * =========
32: *
33: * N (input) INTEGER
34: * The number of linear equations, i.e., the order of the
35: * matrix A. N >= 0.
36: *
37: * NRHS (input) INTEGER
38: * The number of right hand sides, i.e., the number of columns
39: * of the matrix B. NRHS >= 0.
40: *
41: * A (input/output) COMPLEX*16 array, dimension (LDA,N)
42: * On entry, the N-by-N coefficient matrix A.
43: * On exit, the factors L and U from the factorization
44: * A = P*L*U; the unit diagonal elements of L are not stored.
45: *
46: * LDA (input) INTEGER
47: * The leading dimension of the array A. LDA >= max(1,N).
48: *
49: * IPIV (output) INTEGER array, dimension (N)
50: * The pivot indices that define the permutation matrix P;
51: * row i of the matrix was interchanged with row IPIV(i).
52: *
53: * B (input/output) COMPLEX*16 array, dimension (LDB,NRHS)
54: * On entry, the N-by-NRHS matrix of right hand side matrix B.
55: * On exit, if INFO = 0, the N-by-NRHS solution matrix X.
56: *
57: * LDB (input) INTEGER
58: * The leading dimension of the array B. LDB >= max(1,N).
59: *
60: * INFO (output) INTEGER
61: * = 0: successful exit
62: * < 0: if INFO = -i, the i-th argument had an illegal value
63: * > 0: if INFO = i, U(i,i) is exactly zero. The factorization
64: * has been completed, but the factor U is exactly
65: * singular, so the solution could not be computed.
66: *
67: * =====================================================================
68: *
69: * .. External Subroutines ..
70: EXTERNAL XERBLA, ZGETRF, ZGETRS
71: * ..
72: * .. Intrinsic Functions ..
73: INTRINSIC MAX
74: * ..
75: * .. Executable Statements ..
76: *
77: * Test the input parameters.
78: *
79: INFO = 0
80: IF( N.LT.0 ) THEN
81: INFO = -1
82: ELSE IF( NRHS.LT.0 ) THEN
83: INFO = -2
84: ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
85: INFO = -4
86: ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
87: INFO = -7
88: END IF
89: IF( INFO.NE.0 ) THEN
90: CALL XERBLA( 'ZGESV ', -INFO )
91: RETURN
92: END IF
93: *
94: * Compute the LU factorization of A.
95: *
96: CALL ZGETRF( N, N, A, LDA, IPIV, INFO )
97: IF( INFO.EQ.0 ) THEN
98: *
99: * Solve the system A*X = B, overwriting B with X.
100: *
101: CALL ZGETRS( 'No transpose', N, NRHS, A, LDA, IPIV, B, LDB,
102: $ INFO )
103: END IF
104: RETURN
105: *
106: * End of ZGESV
107: *
108: END
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