 LAPACK  3.10.1 LAPACK: Linear Algebra PACKage

## ◆ spotrs()

 subroutine spotrs ( character UPLO, integer N, integer NRHS, real, dimension( lda, * ) A, integer LDA, real, dimension( ldb, * ) B, integer LDB, integer INFO )

SPOTRS

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

Purpose:
``` SPOTRS solves a system of linear equations A*X = B with a symmetric
positive definite matrix A using the Cholesky factorization
A = U**T*U or A = L*L**T computed by SPOTRF.```
Parameters
 [in] UPLO ``` UPLO is CHARACTER*1 = 'U': Upper triangle of A is stored; = 'L': Lower triangle of A is stored.``` [in] N ``` N is INTEGER 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] A ``` A is REAL array, dimension (LDA,N) The triangular factor U or L from the Cholesky factorization A = U**T*U or A = L*L**T, as computed by SPOTRF.``` [in] LDA ``` LDA is INTEGER The leading dimension of the array A. LDA >= max(1,N).``` [in,out] B ``` B is REAL array, dimension (LDB,NRHS) On entry, the right hand side matrix B. On exit, the 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```

Definition at line 109 of file spotrs.f.

110 *
111 * -- LAPACK computational routine --
112 * -- LAPACK is a software package provided by Univ. of Tennessee, --
113 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
114 *
115 * .. Scalar Arguments ..
116  CHARACTER UPLO
117  INTEGER INFO, LDA, LDB, N, NRHS
118 * ..
119 * .. Array Arguments ..
120  REAL A( LDA, * ), B( LDB, * )
121 * ..
122 *
123 * =====================================================================
124 *
125 * .. Parameters ..
126  REAL ONE
127  parameter( one = 1.0e+0 )
128 * ..
129 * .. Local Scalars ..
130  LOGICAL UPPER
131 * ..
132 * .. External Functions ..
133  LOGICAL LSAME
134  EXTERNAL lsame
135 * ..
136 * .. External Subroutines ..
137  EXTERNAL strsm, xerbla
138 * ..
139 * .. Intrinsic Functions ..
140  INTRINSIC max
141 * ..
142 * .. Executable Statements ..
143 *
144 * Test the input parameters.
145 *
146  info = 0
147  upper = lsame( uplo, 'U' )
148  IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
149  info = -1
150  ELSE IF( n.LT.0 ) THEN
151  info = -2
152  ELSE IF( nrhs.LT.0 ) THEN
153  info = -3
154  ELSE IF( lda.LT.max( 1, n ) ) THEN
155  info = -5
156  ELSE IF( ldb.LT.max( 1, n ) ) THEN
157  info = -7
158  END IF
159  IF( info.NE.0 ) THEN
160  CALL xerbla( 'SPOTRS', -info )
161  RETURN
162  END IF
163 *
164 * Quick return if possible
165 *
166  IF( n.EQ.0 .OR. nrhs.EQ.0 )
167  \$ RETURN
168 *
169  IF( upper ) THEN
170 *
171 * Solve A*X = B where A = U**T *U.
172 *
173 * Solve U**T *X = B, overwriting B with X.
174 *
175  CALL strsm( 'Left', 'Upper', 'Transpose', 'Non-unit', n, nrhs,
176  \$ one, a, lda, b, ldb )
177 *
178 * Solve U*X = B, overwriting B with X.
179 *
180  CALL strsm( 'Left', 'Upper', 'No transpose', 'Non-unit', n,
181  \$ nrhs, one, a, lda, b, ldb )
182  ELSE
183 *
184 * Solve A*X = B where A = L*L**T.
185 *
186 * Solve L*X = B, overwriting B with X.
187 *
188  CALL strsm( 'Left', 'Lower', 'No transpose', 'Non-unit', n,
189  \$ nrhs, one, a, lda, b, ldb )
190 *
191 * Solve L**T *X = B, overwriting B with X.
192 *
193  CALL strsm( 'Left', 'Lower', 'Transpose', 'Non-unit', n, nrhs,
194  \$ one, a, lda, b, ldb )
195  END IF
196 *
197  RETURN
198 *
199 * End of SPOTRS
200 *
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
subroutine strsm(SIDE, UPLO, TRANSA, DIAG, M, N, ALPHA, A, LDA, B, LDB)
STRSM
Definition: strsm.f:181
Here is the call graph for this function:
Here is the caller graph for this function: