LAPACK 3.12.0
LAPACK: Linear Algebra PACKage
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◆ sgesv()

subroutine sgesv ( integer  n,
integer  nrhs,
real, dimension( lda, * )  a,
integer  lda,
integer, dimension( * )  ipiv,
real, dimension( ldb, * )  b,
integer  ldb,
integer  info 
)

Download SGESV + dependencies [TGZ] [ZIP] [TXT]

Purpose:
 SGESV computes the solution to a real system of linear equations
    A * X = B,
 where A is an N-by-N matrix and X and B are N-by-NRHS matrices.

 The LU decomposition with partial pivoting and row interchanges is
 used to factor A as
    A = P * L * U,
 where P is a permutation matrix, L is unit lower triangular, and U is
 upper triangular.  The factored form of A is then used to solve the
 system of equations A * X = B.
Parameters
[in]N
          N is INTEGER
          The number of linear equations, i.e., the order of the
          matrix A.  N >= 0.
[in]NRHS
          NRHS is INTEGER
          The number of right hand sides, i.e., the number of columns
          of the matrix B.  NRHS >= 0.
[in,out]A
          A is REAL array, dimension (LDA,N)
          On entry, the N-by-N coefficient matrix A.
          On exit, the factors L and U from the factorization
          A = P*L*U; the unit diagonal elements of L are not stored.
[in]LDA
          LDA is INTEGER
          The leading dimension of the array A.  LDA >= max(1,N).
[out]IPIV
          IPIV is INTEGER array, dimension (N)
          The pivot indices that define the permutation matrix P;
          row i of the matrix was interchanged with row IPIV(i).
[in,out]B
          B is REAL array, dimension (LDB,NRHS)
          On entry, the N-by-NRHS matrix of right hand side matrix B.
          On exit, if INFO = 0, the N-by-NRHS solution matrix X.
[in]LDB
          LDB is INTEGER
          The leading dimension of the array B.  LDB >= max(1,N).
[out]INFO
          INFO is INTEGER
          = 0:  successful exit
          < 0:  if INFO = -i, the i-th argument had an illegal value
          > 0:  if INFO = i, U(i,i) is exactly zero.  The factorization
                has been completed, but the factor U is exactly
                singular, so the solution could not be computed.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.

Definition at line 123 of file sgesv.f.

124*
125* -- LAPACK driver routine --
126* -- LAPACK is a software package provided by Univ. of Tennessee, --
127* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
128*
129* .. Scalar Arguments ..
130 INTEGER INFO, LDA, LDB, N, NRHS
131* ..
132* .. Array Arguments ..
133 INTEGER IPIV( * )
134 REAL A( LDA, * ), B( LDB, * )
135* ..
136*
137* =====================================================================
138*
139* .. External Subroutines ..
140 EXTERNAL sgetrf, sgetrs, xerbla
141* ..
142* .. Intrinsic Functions ..
143 INTRINSIC max
144* ..
145* .. Executable Statements ..
146*
147* Test the input parameters.
148*
149 info = 0
150 IF( n.LT.0 ) THEN
151 info = -1
152 ELSE IF( nrhs.LT.0 ) THEN
153 info = -2
154 ELSE IF( lda.LT.max( 1, n ) ) THEN
155 info = -4
156 ELSE IF( ldb.LT.max( 1, n ) ) THEN
157 info = -7
158 END IF
159 IF( info.NE.0 ) THEN
160 CALL xerbla( 'SGESV ', -info )
161 RETURN
162 END IF
163*
164* Compute the LU factorization of A.
165*
166 CALL sgetrf( n, n, a, lda, ipiv, info )
167 IF( info.EQ.0 ) THEN
168*
169* Solve the system A*X = B, overwriting B with X.
170*
171 CALL sgetrs( 'No transpose', n, nrhs, a, lda, ipiv, b, ldb,
172 $ info )
173 END IF
174 RETURN
175*
176* End of SGESV
177*
subroutine xerbla(srname, info)
Definition cblat2.f:3285
subroutine sgetrf(m, n, a, lda, ipiv, info)
SGETRF
Definition sgetrf.f:108
subroutine sgetrs(trans, n, nrhs, a, lda, ipiv, b, ldb, info)
SGETRS
Definition sgetrs.f:121
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