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SUBROUTINE <a name="STPTRS.1"></a><a href="stptrs.f.html#STPTRS.1">STPTRS</a>( UPLO, TRANS, DIAG, N, NRHS, AP, 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 DIAG, TRANS, UPLO
INTEGER INFO, LDB, N, NRHS
<span class="comment">*</span><span class="comment"> ..
</span><span class="comment">*</span><span class="comment"> .. Array Arguments ..
</span> REAL AP( * ), 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="STPTRS.18"></a><a href="stptrs.f.html#STPTRS.1">STPTRS</a> solves a triangular system of the form
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> A * X = B or A**T * X = B,
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> where A is a triangular matrix of order N stored in packed format,
</span><span class="comment">*</span><span class="comment"> and B is an N-by-NRHS matrix. A check is made to verify that A is
</span><span class="comment">*</span><span class="comment"> nonsingular.
</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"> UPLO (input) CHARACTER*1
</span><span class="comment">*</span><span class="comment"> = 'U': A is upper triangular;
</span><span class="comment">*</span><span class="comment"> = 'L': A is lower triangular.
</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 = Transpose)
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> DIAG (input) CHARACTER*1
</span><span class="comment">*</span><span class="comment"> = 'N': A is non-unit triangular;
</span><span class="comment">*</span><span class="comment"> = 'U': A is unit triangular.
</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 >= 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 >= 0.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> AP (input) REAL array, dimension (N*(N+1)/2)
</span><span class="comment">*</span><span class="comment"> The upper or lower triangular matrix A, packed columnwise in
</span><span class="comment">*</span><span class="comment"> a linear array. The j-th column of A is stored in the array
</span><span class="comment">*</span><span class="comment"> AP as follows:
</span><span class="comment">*</span><span class="comment"> if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j;
</span><span class="comment">*</span><span class="comment"> if UPLO = 'L', AP(i + (j-1)*(2*n-j)/2) = A(i,j) for j<=i<=n.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> B (input/output) REAL 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, if INFO = 0, 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 >= 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"> < 0: if INFO = -i, the i-th argument had an illegal value
</span><span class="comment">*</span><span class="comment"> > 0: if INFO = i, the i-th diagonal element of A is zero,
</span><span class="comment">*</span><span class="comment"> indicating that the matrix is singular and the
</span><span class="comment">*</span><span class="comment"> solutions X have not been computed.
</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> REAL ZERO
PARAMETER ( ZERO = 0.0E+0 )
<span class="comment">*</span><span class="comment"> ..
</span><span class="comment">*</span><span class="comment"> .. Local Scalars ..
</span> LOGICAL NOUNIT, UPPER
INTEGER J, JC
<span class="comment">*</span><span class="comment"> ..
</span><span class="comment">*</span><span class="comment"> .. External Functions ..
</span> LOGICAL <a name="LSAME.82"></a><a href="lsame.f.html#LSAME.1">LSAME</a>
EXTERNAL <a name="LSAME.83"></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 STPSV, <a name="XERBLA.86"></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
UPPER = <a name="LSAME.96"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( UPLO, <span class="string">'U'</span> )
NOUNIT = <a name="LSAME.97"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( DIAG, <span class="string">'N'</span> )
IF( .NOT.UPPER .AND. .NOT.<a name="LSAME.98"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( UPLO, <span class="string">'L'</span> ) ) THEN
INFO = -1
ELSE IF( .NOT.<a name="LSAME.100"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( TRANS, <span class="string">'N'</span> ) .AND. .NOT.
$ <a name="LSAME.101"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( TRANS, <span class="string">'T'</span> ) .AND. .NOT.<a name="LSAME.101"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( TRANS, <span class="string">'C'</span> ) ) THEN
INFO = -2
ELSE IF( .NOT.NOUNIT .AND. .NOT.<a name="LSAME.103"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( DIAG, <span class="string">'U'</span> ) ) THEN
INFO = -3
ELSE IF( N.LT.0 ) THEN
INFO = -4
ELSE IF( NRHS.LT.0 ) THEN
INFO = -5
ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
INFO = -8
END IF
IF( INFO.NE.0 ) THEN
CALL <a name="XERBLA.113"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>( <span class="string">'<a name="STPTRS.113"></a><a href="stptrs.f.html#STPTRS.1">STPTRS</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 )
$ RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> Check for singularity.
</span><span class="comment">*</span><span class="comment">
</span> IF( NOUNIT ) THEN
IF( UPPER ) THEN
JC = 1
DO 10 INFO = 1, N
IF( AP( JC+INFO-1 ).EQ.ZERO )
$ RETURN
JC = JC + INFO
10 CONTINUE
ELSE
JC = 1
DO 20 INFO = 1, N
IF( AP( JC ).EQ.ZERO )
$ RETURN
JC = JC + N - INFO + 1
20 CONTINUE
END IF
END IF
INFO = 0
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> Solve A * x = b or A' * x = b.
</span><span class="comment">*</span><span class="comment">
</span> DO 30 J = 1, NRHS
CALL STPSV( UPLO, TRANS, DIAG, N, AP, B( 1, J ), 1 )
30 CONTINUE
<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="STPTRS.151"></a><a href="stptrs.f.html#STPTRS.1">STPTRS</a>
</span><span class="comment">*</span><span class="comment">
</span> END
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