LAPACK 3.11.0
LAPACK: Linear Algebra PACKage
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◆ dtptrs()

subroutine dtptrs ( character  UPLO,
character  TRANS,
character  DIAG,
integer  N,
integer  NRHS,
double precision, dimension( * )  AP,
double precision, dimension( ldb, * )  B,
integer  LDB,
integer  INFO 
)

DTPTRS

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

Purpose:
 DTPTRS solves a triangular system of the form

    A * X = B  or  A**T * X = B,

 where A is a triangular matrix of order N stored in packed format,
 and B is an N-by-NRHS matrix.  A check is made to verify that A is
 nonsingular.
Parameters
[in]UPLO
          UPLO is CHARACTER*1
          = 'U':  A is upper triangular;
          = 'L':  A is lower triangular.
[in]TRANS
          TRANS is CHARACTER*1
          Specifies the form of the system of equations:
          = 'N':  A * X = B  (No transpose)
          = 'T':  A**T * X = B  (Transpose)
          = 'C':  A**H * X = B  (Conjugate transpose = Transpose)
[in]DIAG
          DIAG is CHARACTER*1
          = 'N':  A is non-unit triangular;
          = 'U':  A is unit triangular.
[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]AP
          AP is DOUBLE PRECISION array, dimension (N*(N+1)/2)
          The upper or lower triangular matrix A, packed columnwise in
          a linear array.  The j-th column of A is stored in the array
          AP as follows:
          if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j;
          if UPLO = 'L', AP(i + (j-1)*(2*n-j)/2) = A(i,j) for j<=i<=n.
[in,out]B
          B is DOUBLE PRECISION array, dimension (LDB,NRHS)
          On entry, the right hand side matrix B.
          On exit, if INFO = 0, 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
          > 0:  if INFO = i, the i-th diagonal element of A is zero,
                indicating that the matrix is singular and the
                solutions X have not been computed.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.

Definition at line 129 of file dtptrs.f.

130*
131* -- LAPACK computational routine --
132* -- LAPACK is a software package provided by Univ. of Tennessee, --
133* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
134*
135* .. Scalar Arguments ..
136 CHARACTER DIAG, TRANS, UPLO
137 INTEGER INFO, LDB, N, NRHS
138* ..
139* .. Array Arguments ..
140 DOUBLE PRECISION AP( * ), B( LDB, * )
141* ..
142*
143* =====================================================================
144*
145* .. Parameters ..
146 DOUBLE PRECISION ZERO
147 parameter( zero = 0.0d+0 )
148* ..
149* .. Local Scalars ..
150 LOGICAL NOUNIT, UPPER
151 INTEGER J, JC
152* ..
153* .. External Functions ..
154 LOGICAL LSAME
155 EXTERNAL lsame
156* ..
157* .. External Subroutines ..
158 EXTERNAL dtpsv, xerbla
159* ..
160* .. Intrinsic Functions ..
161 INTRINSIC max
162* ..
163* .. Executable Statements ..
164*
165* Test the input parameters.
166*
167 info = 0
168 upper = lsame( uplo, 'U' )
169 nounit = lsame( diag, 'N' )
170 IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
171 info = -1
172 ELSE IF( .NOT.lsame( trans, 'N' ) .AND. .NOT.
173 $ lsame( trans, 'T' ) .AND. .NOT.lsame( trans, 'C' ) ) THEN
174 info = -2
175 ELSE IF( .NOT.nounit .AND. .NOT.lsame( diag, 'U' ) ) THEN
176 info = -3
177 ELSE IF( n.LT.0 ) THEN
178 info = -4
179 ELSE IF( nrhs.LT.0 ) THEN
180 info = -5
181 ELSE IF( ldb.LT.max( 1, n ) ) THEN
182 info = -8
183 END IF
184 IF( info.NE.0 ) THEN
185 CALL xerbla( 'DTPTRS', -info )
186 RETURN
187 END IF
188*
189* Quick return if possible
190*
191 IF( n.EQ.0 )
192 $ RETURN
193*
194* Check for singularity.
195*
196 IF( nounit ) THEN
197 IF( upper ) THEN
198 jc = 1
199 DO 10 info = 1, n
200 IF( ap( jc+info-1 ).EQ.zero )
201 $ RETURN
202 jc = jc + info
203 10 CONTINUE
204 ELSE
205 jc = 1
206 DO 20 info = 1, n
207 IF( ap( jc ).EQ.zero )
208 $ RETURN
209 jc = jc + n - info + 1
210 20 CONTINUE
211 END IF
212 END IF
213 info = 0
214*
215* Solve A * x = b or A**T * x = b.
216*
217 DO 30 j = 1, nrhs
218 CALL dtpsv( uplo, trans, diag, n, ap, b( 1, j ), 1 )
219 30 CONTINUE
220*
221 RETURN
222*
223* End of DTPTRS
224*
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
subroutine dtpsv(UPLO, TRANS, DIAG, N, AP, X, INCX)
DTPSV
Definition: dtpsv.f:144
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