LAPACK 3.11.0
LAPACK: Linear Algebra PACKage
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◆ dptsv()

subroutine dptsv ( integer  N,
integer  NRHS,
double precision, dimension( * )  D,
double precision, dimension( * )  E,
double precision, dimension( ldb, * )  B,
integer  LDB,
integer  INFO 
)

DPTSV computes the solution to system of linear equations A * X = B for PT matrices

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

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

 A is factored as A = L*D*L**T, and the factored form of A is then
 used to solve the system of equations.
Parameters
[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,out]D
          D is DOUBLE PRECISION array, dimension (N)
          On entry, the n diagonal elements of the tridiagonal matrix
          A.  On exit, the n diagonal elements of the diagonal matrix
          D from the factorization A = L*D*L**T.
[in,out]E
          E is DOUBLE PRECISION array, dimension (N-1)
          On entry, the (n-1) subdiagonal elements of the tridiagonal
          matrix A.  On exit, the (n-1) subdiagonal elements of the
          unit bidiagonal factor L from the L*D*L**T factorization of
          A.  (E can also be regarded as the superdiagonal of the unit
          bidiagonal factor U from the U**T*D*U factorization of A.)
[in,out]B
          B is DOUBLE PRECISION array, dimension (LDB,NRHS)
          On entry, the N-by-NRHS 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, the leading minor of order i is not
                positive definite, and the solution has not been
                computed.  The factorization has not been completed
                unless i = N.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.

Definition at line 113 of file dptsv.f.

114*
115* -- LAPACK driver routine --
116* -- LAPACK is a software package provided by Univ. of Tennessee, --
117* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
118*
119* .. Scalar Arguments ..
120 INTEGER INFO, LDB, N, NRHS
121* ..
122* .. Array Arguments ..
123 DOUBLE PRECISION B( LDB, * ), D( * ), E( * )
124* ..
125*
126* =====================================================================
127*
128* .. External Subroutines ..
129 EXTERNAL dpttrf, dpttrs, xerbla
130* ..
131* .. Intrinsic Functions ..
132 INTRINSIC max
133* ..
134* .. Executable Statements ..
135*
136* Test the input parameters.
137*
138 info = 0
139 IF( n.LT.0 ) THEN
140 info = -1
141 ELSE IF( nrhs.LT.0 ) THEN
142 info = -2
143 ELSE IF( ldb.LT.max( 1, n ) ) THEN
144 info = -6
145 END IF
146 IF( info.NE.0 ) THEN
147 CALL xerbla( 'DPTSV ', -info )
148 RETURN
149 END IF
150*
151* Compute the L*D*L**T (or U**T*D*U) factorization of A.
152*
153 CALL dpttrf( n, d, e, info )
154 IF( info.EQ.0 ) THEN
155*
156* Solve the system A*X = B, overwriting B with X.
157*
158 CALL dpttrs( n, nrhs, d, e, b, ldb, info )
159 END IF
160 RETURN
161*
162* End of DPTSV
163*
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
subroutine dpttrf(N, D, E, INFO)
DPTTRF
Definition: dpttrf.f:91
subroutine dpttrs(N, NRHS, D, E, B, LDB, INFO)
DPTTRS
Definition: dpttrs.f:109
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