LAPACK 3.12.0
LAPACK: Linear Algebra PACKage
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◆ dpptrs()

subroutine dpptrs ( character  uplo,
integer  n,
integer  nrhs,
double precision, dimension( * )  ap,
double precision, dimension( ldb, * )  b,
integer  ldb,
integer  info 
)

DPPTRS

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

Purpose:
 DPPTRS solves a system of linear equations A*X = B with a symmetric
 positive definite matrix A in packed storage using the Cholesky
 factorization A = U**T*U or A = L*L**T computed by DPPTRF.
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]AP
          AP is DOUBLE PRECISION array, dimension (N*(N+1)/2)
          The triangular factor U or L from the Cholesky factorization
          A = U**T*U or A = L*L**T, packed columnwise in a linear
          array.  The j-th column of U or L is stored in the array AP
          as follows:
          if UPLO = 'U', AP(i + (j-1)*j/2) = U(i,j) for 1<=i<=j;
          if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = L(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, 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
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.

Definition at line 107 of file dpptrs.f.

108*
109* -- LAPACK computational routine --
110* -- LAPACK is a software package provided by Univ. of Tennessee, --
111* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
112*
113* .. Scalar Arguments ..
114 CHARACTER UPLO
115 INTEGER INFO, LDB, N, NRHS
116* ..
117* .. Array Arguments ..
118 DOUBLE PRECISION AP( * ), B( LDB, * )
119* ..
120*
121* =====================================================================
122*
123* .. Local Scalars ..
124 LOGICAL UPPER
125 INTEGER I
126* ..
127* .. External Functions ..
128 LOGICAL LSAME
129 EXTERNAL lsame
130* ..
131* .. External Subroutines ..
132 EXTERNAL dtpsv, xerbla
133* ..
134* .. Intrinsic Functions ..
135 INTRINSIC max
136* ..
137* .. Executable Statements ..
138*
139* Test the input parameters.
140*
141 info = 0
142 upper = lsame( uplo, 'U' )
143 IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
144 info = -1
145 ELSE IF( n.LT.0 ) THEN
146 info = -2
147 ELSE IF( nrhs.LT.0 ) THEN
148 info = -3
149 ELSE IF( ldb.LT.max( 1, n ) ) THEN
150 info = -6
151 END IF
152 IF( info.NE.0 ) THEN
153 CALL xerbla( 'DPPTRS', -info )
154 RETURN
155 END IF
156*
157* Quick return if possible
158*
159 IF( n.EQ.0 .OR. nrhs.EQ.0 )
160 $ RETURN
161*
162 IF( upper ) THEN
163*
164* Solve A*X = B where A = U**T * U.
165*
166 DO 10 i = 1, nrhs
167*
168* Solve U**T *X = B, overwriting B with X.
169*
170 CALL dtpsv( 'Upper', 'Transpose', 'Non-unit', n, ap,
171 $ b( 1, i ), 1 )
172*
173* Solve U*X = B, overwriting B with X.
174*
175 CALL dtpsv( 'Upper', 'No transpose', 'Non-unit', n, ap,
176 $ b( 1, i ), 1 )
177 10 CONTINUE
178 ELSE
179*
180* Solve A*X = B where A = L * L**T.
181*
182 DO 20 i = 1, nrhs
183*
184* Solve L*Y = B, overwriting B with X.
185*
186 CALL dtpsv( 'Lower', 'No transpose', 'Non-unit', n, ap,
187 $ b( 1, i ), 1 )
188*
189* Solve L**T *X = Y, overwriting B with X.
190*
191 CALL dtpsv( 'Lower', 'Transpose', 'Non-unit', n, ap,
192 $ b( 1, i ), 1 )
193 20 CONTINUE
194 END IF
195*
196 RETURN
197*
198* End of DPPTRS
199*
subroutine xerbla(srname, info)
Definition cblat2.f:3285
logical function lsame(ca, cb)
LSAME
Definition lsame.f:48
subroutine dtpsv(uplo, trans, diag, n, ap, x, incx)
DTPSV
Definition dtpsv.f:144
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