LAPACK  3.10.0
LAPACK: Linear Algebra PACKage

◆ 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

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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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