```      SUBROUTINE DPOTRS( UPLO, N, NRHS, A, LDA, B, LDB, INFO )
*
*  -- LAPACK routine (version 3.1) --
*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
*     November 2006
*
*     .. Scalar Arguments ..
CHARACTER          UPLO
INTEGER            INFO, LDA, LDB, N, NRHS
*     ..
*     .. Array Arguments ..
DOUBLE PRECISION   A( LDA, * ), B( LDB, * )
*     ..
*
*  Purpose
*  =======
*
*  DPOTRS 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 DPOTRF.
*
*  Arguments
*  =========
*
*  UPLO    (input) CHARACTER*1
*          = 'U':  Upper triangle of A is stored;
*          = 'L':  Lower triangle of A is stored.
*
*  N       (input) INTEGER
*          The order of the matrix A.  N >= 0.
*
*  NRHS    (input) INTEGER
*          The number of right hand sides, i.e., the number of columns
*          of the matrix B.  NRHS >= 0.
*
*  A       (input) DOUBLE PRECISION 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 DPOTRF.
*
*  LDA     (input) INTEGER
*          The leading dimension of the array A.  LDA >= max(1,N).
*
*  B       (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
*          On entry, the right hand side matrix B.
*          On exit, the solution matrix X.
*
*  LDB     (input) INTEGER
*          The leading dimension of the array B.  LDB >= max(1,N).
*
*  INFO    (output) INTEGER
*          = 0:  successful exit
*          < 0:  if INFO = -i, the i-th argument had an illegal value
*
*  =====================================================================
*
*     .. Parameters ..
DOUBLE PRECISION   ONE
PARAMETER          ( ONE = 1.0D+0 )
*     ..
*     .. Local Scalars ..
LOGICAL            UPPER
*     ..
*     .. External Functions ..
LOGICAL            LSAME
EXTERNAL           LSAME
*     ..
*     .. External Subroutines ..
EXTERNAL           DTRSM, XERBLA
*     ..
*     .. Intrinsic Functions ..
INTRINSIC          MAX
*     ..
*     .. Executable Statements ..
*
*     Test the input parameters.
*
INFO = 0
UPPER = LSAME( UPLO, 'U' )
IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
INFO = -1
ELSE IF( N.LT.0 ) THEN
INFO = -2
ELSE IF( NRHS.LT.0 ) THEN
INFO = -3
ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
INFO = -5
ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
INFO = -7
END IF
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'DPOTRS', -INFO )
RETURN
END IF
*
*     Quick return if possible
*
IF( N.EQ.0 .OR. NRHS.EQ.0 )
\$   RETURN
*
IF( UPPER ) THEN
*
*        Solve A*X = B where A = U'*U.
*
*        Solve U'*X = B, overwriting B with X.
*
CALL DTRSM( 'Left', 'Upper', 'Transpose', 'Non-unit', N, NRHS,
\$               ONE, A, LDA, B, LDB )
*
*        Solve U*X = B, overwriting B with X.
*
CALL DTRSM( 'Left', 'Upper', 'No transpose', 'Non-unit', N,
\$               NRHS, ONE, A, LDA, B, LDB )
ELSE
*
*        Solve A*X = B where A = L*L'.
*
*        Solve L*X = B, overwriting B with X.
*
CALL DTRSM( 'Left', 'Lower', 'No transpose', 'Non-unit', N,
\$               NRHS, ONE, A, LDA, B, LDB )
*
*        Solve L'*X = B, overwriting B with X.
*
CALL DTRSM( 'Left', 'Lower', 'Transpose', 'Non-unit', N, NRHS,
\$               ONE, A, LDA, B, LDB )
END IF
*
RETURN
*
*     End of DPOTRS
*
END

```