00001 SUBROUTINE DGESV( N, NRHS, A, LDA, IPIV, B, LDB, INFO ) 00002 * 00003 * -- LAPACK driver routine (version 3.2) -- 00004 * -- LAPACK is a software package provided by Univ. of Tennessee, -- 00005 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- 00006 * November 2006 00007 * 00008 * .. Scalar Arguments .. 00009 INTEGER INFO, LDA, LDB, N, NRHS 00010 * .. 00011 * .. Array Arguments .. 00012 INTEGER IPIV( * ) 00013 DOUBLE PRECISION A( LDA, * ), B( LDB, * ) 00014 * .. 00015 * 00016 * Purpose 00017 * ======= 00018 * 00019 * DGESV computes the solution to a real system of linear equations 00020 * A * X = B, 00021 * where A is an N-by-N matrix and X and B are N-by-NRHS matrices. 00022 * 00023 * The LU decomposition with partial pivoting and row interchanges is 00024 * used to factor A as 00025 * A = P * L * U, 00026 * where P is a permutation matrix, L is unit lower triangular, and U is 00027 * upper triangular. The factored form of A is then used to solve the 00028 * system of equations A * X = B. 00029 * 00030 * Arguments 00031 * ========= 00032 * 00033 * N (input) INTEGER 00034 * The number of linear equations, i.e., the order of the 00035 * matrix A. N >= 0. 00036 * 00037 * NRHS (input) INTEGER 00038 * The number of right hand sides, i.e., the number of columns 00039 * of the matrix B. NRHS >= 0. 00040 * 00041 * A (input/output) DOUBLE PRECISION array, dimension (LDA,N) 00042 * On entry, the N-by-N coefficient matrix A. 00043 * On exit, the factors L and U from the factorization 00044 * A = P*L*U; the unit diagonal elements of L are not stored. 00045 * 00046 * LDA (input) INTEGER 00047 * The leading dimension of the array A. LDA >= max(1,N). 00048 * 00049 * IPIV (output) INTEGER array, dimension (N) 00050 * The pivot indices that define the permutation matrix P; 00051 * row i of the matrix was interchanged with row IPIV(i). 00052 * 00053 * B (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS) 00054 * On entry, the N-by-NRHS matrix of right hand side matrix B. 00055 * On exit, if INFO = 0, the N-by-NRHS solution matrix X. 00056 * 00057 * LDB (input) INTEGER 00058 * The leading dimension of the array B. LDB >= max(1,N). 00059 * 00060 * INFO (output) INTEGER 00061 * = 0: successful exit 00062 * < 0: if INFO = -i, the i-th argument had an illegal value 00063 * > 0: if INFO = i, U(i,i) is exactly zero. The factorization 00064 * has been completed, but the factor U is exactly 00065 * singular, so the solution could not be computed. 00066 * 00067 * ===================================================================== 00068 * 00069 * .. External Subroutines .. 00070 EXTERNAL DGETRF, DGETRS, XERBLA 00071 * .. 00072 * .. Intrinsic Functions .. 00073 INTRINSIC MAX 00074 * .. 00075 * .. Executable Statements .. 00076 * 00077 * Test the input parameters. 00078 * 00079 INFO = 0 00080 IF( N.LT.0 ) THEN 00081 INFO = -1 00082 ELSE IF( NRHS.LT.0 ) THEN 00083 INFO = -2 00084 ELSE IF( LDA.LT.MAX( 1, N ) ) THEN 00085 INFO = -4 00086 ELSE IF( LDB.LT.MAX( 1, N ) ) THEN 00087 INFO = -7 00088 END IF 00089 IF( INFO.NE.0 ) THEN 00090 CALL XERBLA( 'DGESV ', -INFO ) 00091 RETURN 00092 END IF 00093 * 00094 * Compute the LU factorization of A. 00095 * 00096 CALL DGETRF( N, N, A, LDA, IPIV, INFO ) 00097 IF( INFO.EQ.0 ) THEN 00098 * 00099 * Solve the system A*X = B, overwriting B with X. 00100 * 00101 CALL DGETRS( 'No transpose', N, NRHS, A, LDA, IPIV, B, LDB, 00102 $ INFO ) 00103 END IF 00104 RETURN 00105 * 00106 * End of DGESV 00107 * 00108 END
1.7.2