cgetrs.f.html

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      SUBROUTINE <a name="CGETRS.1"></a><a href="cgetrs.f.html#CGETRS.1">CGETRS</a>( TRANS, N, NRHS, A, LDA, IPIV, B, LDB, INFO )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  -- LAPACK routine (version 3.1) --
</span><span class="comment">*</span><span class="comment">     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
</span><span class="comment">*</span><span class="comment">     November 2006
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     .. Scalar Arguments ..
</span>      CHARACTER          TRANS
      INTEGER            INFO, LDA, LDB, N, NRHS
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Array Arguments ..
</span>      INTEGER            IPIV( * )
      COMPLEX            A( LDA, * ), B( LDB, * )
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Purpose
</span><span class="comment">*</span><span class="comment">  =======
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  <a name="CGETRS.19"></a><a href="cgetrs.f.html#CGETRS.1">CGETRS</a> solves a system of linear equations
</span><span class="comment">*</span><span class="comment">     A * X = B,  A**T * X = B,  or  A**H * X = B
</span><span class="comment">*</span><span class="comment">  with a general N-by-N matrix A using the LU factorization computed
</span><span class="comment">*</span><span class="comment">  by <a name="CGETRF.22"></a><a href="cgetrf.f.html#CGETRF.1">CGETRF</a>.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Arguments
</span><span class="comment">*</span><span class="comment">  =========
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  TRANS   (input) CHARACTER*1
</span><span class="comment">*</span><span class="comment">          Specifies the form of the system of equations:
</span><span class="comment">*</span><span class="comment">          = 'N':  A * X = B     (No transpose)
</span><span class="comment">*</span><span class="comment">          = 'T':  A**T * X = B  (Transpose)
</span><span class="comment">*</span><span class="comment">          = 'C':  A**H * X = B  (Conjugate transpose)
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  N       (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The order of the matrix A.  N &gt;= 0.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  NRHS    (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The number of right hand sides, i.e., the number of columns
</span><span class="comment">*</span><span class="comment">          of the matrix B.  NRHS &gt;= 0.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  A       (input) COMPLEX array, dimension (LDA,N)
</span><span class="comment">*</span><span class="comment">          The factors L and U from the factorization A = P*L*U
</span><span class="comment">*</span><span class="comment">          as computed by <a name="CGETRF.42"></a><a href="cgetrf.f.html#CGETRF.1">CGETRF</a>.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  LDA     (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The leading dimension of the array A.  LDA &gt;= max(1,N).
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  IPIV    (input) INTEGER array, dimension (N)
</span><span class="comment">*</span><span class="comment">          The pivot indices from <a name="CGETRF.48"></a><a href="cgetrf.f.html#CGETRF.1">CGETRF</a>; for 1&lt;=i&lt;=N, row i of the
</span><span class="comment">*</span><span class="comment">          matrix was interchanged with row IPIV(i).
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  B       (input/output) COMPLEX array, dimension (LDB,NRHS)
</span><span class="comment">*</span><span class="comment">          On entry, the right hand side matrix B.
</span><span class="comment">*</span><span class="comment">          On exit, the solution matrix X.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  LDB     (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The leading dimension of the array B.  LDB &gt;= max(1,N).
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  INFO    (output) INTEGER
</span><span class="comment">*</span><span class="comment">          = 0:  successful exit
</span><span class="comment">*</span><span class="comment">          &lt; 0:  if INFO = -i, the i-th argument had an illegal value
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  =====================================================================
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     .. Parameters ..
</span>      COMPLEX            ONE
      PARAMETER          ( ONE = ( 1.0E+0, 0.0E+0 ) )
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Local Scalars ..
</span>      LOGICAL            NOTRAN
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. External Functions ..
</span>      LOGICAL            <a name="LSAME.72"></a><a href="lsame.f.html#LSAME.1">LSAME</a>
      EXTERNAL           <a name="LSAME.73"></a><a href="lsame.f.html#LSAME.1">LSAME</a>
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. External Subroutines ..
</span>      EXTERNAL           <a name="CLASWP.76"></a><a href="claswp.f.html#CLASWP.1">CLASWP</a>, CTRSM, <a name="XERBLA.76"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Intrinsic Functions ..
</span>      INTRINSIC          MAX
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Executable Statements ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Test the input parameters.
</span><span class="comment">*</span><span class="comment">
</span>      INFO = 0
      NOTRAN = <a name="LSAME.86"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( TRANS, <span class="string">'N'</span> )
      IF( .NOT.NOTRAN .AND. .NOT.<a name="LSAME.87"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( TRANS, <span class="string">'T'</span> ) .AND. .NOT.
     $    <a name="LSAME.88"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( TRANS, <span class="string">'C'</span> ) ) 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 = -8
      END IF
      IF( INFO.NE.0 ) THEN
         CALL <a name="XERBLA.100"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>( <span class="string">'<a name="CGETRS.100"></a><a href="cgetrs.f.html#CGETRS.1">CGETRS</a>'</span>, -INFO )
         RETURN
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Quick return if possible
</span><span class="comment">*</span><span class="comment">
</span>      IF( N.EQ.0 .OR. NRHS.EQ.0 )
     $   RETURN
<span class="comment">*</span><span class="comment">
</span>      IF( NOTRAN ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Solve A * X = B.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Apply row interchanges to the right hand sides.
</span><span class="comment">*</span><span class="comment">
</span>         CALL <a name="CLASWP.115"></a><a href="claswp.f.html#CLASWP.1">CLASWP</a>( NRHS, B, LDB, 1, N, IPIV, 1 )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Solve L*X = B, overwriting B with X.
</span><span class="comment">*</span><span class="comment">
</span>         CALL CTRSM( <span class="string">'Left'</span>, <span class="string">'Lower'</span>, <span class="string">'No transpose'</span>, <span class="string">'Unit'</span>, N, NRHS,
     $               ONE, A, LDA, B, LDB )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Solve U*X = B, overwriting B with X.
</span><span class="comment">*</span><span class="comment">
</span>         CALL CTRSM( <span class="string">'Left'</span>, <span class="string">'Upper'</span>, <span class="string">'No transpose'</span>, <span class="string">'Non-unit'</span>, N,
     $               NRHS, ONE, A, LDA, B, LDB )
      ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Solve A**T * X = B  or A**H * X = B.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Solve U'*X = B, overwriting B with X.
</span><span class="comment">*</span><span class="comment">
</span>         CALL CTRSM( <span class="string">'Left'</span>, <span class="string">'Upper'</span>, TRANS, <span class="string">'Non-unit'</span>, N, NRHS, ONE,
     $               A, LDA, B, LDB )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Solve L'*X = B, overwriting B with X.
</span><span class="comment">*</span><span class="comment">
</span>         CALL CTRSM( <span class="string">'Left'</span>, <span class="string">'Lower'</span>, TRANS, <span class="string">'Unit'</span>, N, NRHS, ONE, A,
     $               LDA, B, LDB )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Apply row interchanges to the solution vectors.
</span><span class="comment">*</span><span class="comment">
</span>         CALL <a name="CLASWP.142"></a><a href="claswp.f.html#CLASWP.1">CLASWP</a>( NRHS, B, LDB, 1, N, IPIV, -1 )
      END IF
<span class="comment">*</span><span class="comment">
</span>      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     End of <a name="CGETRS.147"></a><a href="cgetrs.f.html#CGETRS.1">CGETRS</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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