*> \brief \b STPQRT2 computes a QR factorization of a real or complex "triangular-pentagonal" matrix, which is composed of a triangular block and a pentagonal block, using the compact WY representation for Q. * * =========== DOCUMENTATION =========== * * Online html documentation available at * http://www.netlib.org/lapack/explore-html/ * *> \htmlonly *> Download STPQRT2 + dependencies *> *> [TGZ] *> *> [ZIP] *> *> [TXT] *> \endhtmlonly * * Definition: * =========== * * SUBROUTINE STPQRT2( M, N, L, A, LDA, B, LDB, T, LDT, INFO ) * * .. Scalar Arguments .. * INTEGER INFO, LDA, LDB, LDT, N, M, L * .. * .. Array Arguments .. * REAL A( LDA, * ), B( LDB, * ), T( LDT, * ) * .. * * *> \par Purpose: * ============= *> *> \verbatim *> *> STPQRT2 computes a QR factorization of a real "triangular-pentagonal" *> matrix C, which is composed of a triangular block A and pentagonal block B, *> using the compact WY representation for Q. *> \endverbatim * * Arguments: * ========== * *> \param[in] M *> \verbatim *> M is INTEGER *> The total number of rows of the matrix B. *> M >= 0. *> \endverbatim *> *> \param[in] N *> \verbatim *> N is INTEGER *> The number of columns of the matrix B, and the order of *> the triangular matrix A. *> N >= 0. *> \endverbatim *> *> \param[in] L *> \verbatim *> L is INTEGER *> The number of rows of the upper trapezoidal part of B. *> MIN(M,N) >= L >= 0. See Further Details. *> \endverbatim *> *> \param[in,out] A *> \verbatim *> A is REAL array, dimension (LDA,N) *> On entry, the upper triangular N-by-N matrix A. *> On exit, the elements on and above the diagonal of the array *> contain the upper triangular matrix R. *> \endverbatim *> *> \param[in] LDA *> \verbatim *> LDA is INTEGER *> The leading dimension of the array A. LDA >= max(1,N). *> \endverbatim *> *> \param[in,out] B *> \verbatim *> B is REAL array, dimension (LDB,N) *> On entry, the pentagonal M-by-N matrix B. The first M-L rows *> are rectangular, and the last L rows are upper trapezoidal. *> On exit, B contains the pentagonal matrix V. See Further Details. *> \endverbatim *> *> \param[in] LDB *> \verbatim *> LDB is INTEGER *> The leading dimension of the array B. LDB >= max(1,M). *> \endverbatim *> *> \param[out] T *> \verbatim *> T is REAL array, dimension (LDT,N) *> The N-by-N upper triangular factor T of the block reflector. *> See Further Details. *> \endverbatim *> *> \param[in] LDT *> \verbatim *> LDT is INTEGER *> The leading dimension of the array T. LDT >= max(1,N) *> \endverbatim *> *> \param[out] INFO *> \verbatim *> INFO is INTEGER *> = 0: successful exit *> < 0: if INFO = -i, the i-th argument had an illegal value *> \endverbatim * * Authors: * ======== * *> \author Univ. of Tennessee *> \author Univ. of California Berkeley *> \author Univ. of Colorado Denver *> \author NAG Ltd. * *> \ingroup realOTHERcomputational * *> \par Further Details: * ===================== *> *> \verbatim *> *> The input matrix C is a (N+M)-by-N matrix *> *> C = [ A ] *> [ B ] *> *> where A is an upper triangular N-by-N matrix, and B is M-by-N pentagonal *> matrix consisting of a (M-L)-by-N rectangular matrix B1 on top of a L-by-N *> upper trapezoidal matrix B2: *> *> B = [ B1 ] <- (M-L)-by-N rectangular *> [ B2 ] <- L-by-N upper trapezoidal. *> *> The upper trapezoidal matrix B2 consists of the first L rows of a *> N-by-N upper triangular matrix, where 0 <= L <= MIN(M,N). If L=0, *> B is rectangular M-by-N; if M=L=N, B is upper triangular. *> *> The matrix W stores the elementary reflectors H(i) in the i-th column *> below the diagonal (of A) in the (N+M)-by-N input matrix C *> *> C = [ A ] <- upper triangular N-by-N *> [ B ] <- M-by-N pentagonal *> *> so that W can be represented as *> *> W = [ I ] <- identity, N-by-N *> [ V ] <- M-by-N, same form as B. *> *> Thus, all of information needed for W is contained on exit in B, which *> we call V above. Note that V has the same form as B; that is, *> *> V = [ V1 ] <- (M-L)-by-N rectangular *> [ V2 ] <- L-by-N upper trapezoidal. *> *> The columns of V represent the vectors which define the H(i)'s. *> The (M+N)-by-(M+N) block reflector H is then given by *> *> H = I - W * T * W^H *> *> where W^H is the conjugate transpose of W and T is the upper triangular *> factor of the block reflector. *> \endverbatim *> * ===================================================================== SUBROUTINE STPQRT2( M, N, L, A, LDA, B, LDB, T, LDT, INFO ) * * -- LAPACK computational routine -- * -- LAPACK is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * * .. Scalar Arguments .. INTEGER INFO, LDA, LDB, LDT, N, M, L * .. * .. Array Arguments .. REAL A( LDA, * ), B( LDB, * ), T( LDT, * ) * .. * * ===================================================================== * * .. Parameters .. REAL ONE, ZERO PARAMETER( ONE = 1.0, ZERO = 0.0 ) * .. * .. Local Scalars .. INTEGER I, J, P, MP, NP REAL ALPHA * .. * .. External Subroutines .. EXTERNAL SLARFG, SGEMV, SGER, STRMV, XERBLA * .. * .. Intrinsic Functions .. INTRINSIC MAX, MIN * .. * .. Executable Statements .. * * Test the input arguments * INFO = 0 IF( M.LT.0 ) THEN INFO = -1 ELSE IF( N.LT.0 ) THEN INFO = -2 ELSE IF( L.LT.0 .OR. L.GT.MIN(M,N) ) THEN INFO = -3 ELSE IF( LDA.LT.MAX( 1, N ) ) THEN INFO = -5 ELSE IF( LDB.LT.MAX( 1, M ) ) THEN INFO = -7 ELSE IF( LDT.LT.MAX( 1, N ) ) THEN INFO = -9 END IF IF( INFO.NE.0 ) THEN CALL XERBLA( 'STPQRT2', -INFO ) RETURN END IF * * Quick return if possible * IF( N.EQ.0 .OR. M.EQ.0 ) RETURN * DO I = 1, N * * Generate elementary reflector H(I) to annihilate B(:,I) * P = M-L+MIN( L, I ) CALL SLARFG( P+1, A( I, I ), B( 1, I ), 1, T( I, 1 ) ) IF( I.LT.N ) THEN * * W(1:N-I) := C(I:M,I+1:N)^H * C(I:M,I) [use W = T(:,N)] * DO J = 1, N-I T( J, N ) = (A( I, I+J )) END DO CALL SGEMV( 'T', P, N-I, ONE, B( 1, I+1 ), LDB, \$ B( 1, I ), 1, ONE, T( 1, N ), 1 ) * * C(I:M,I+1:N) = C(I:m,I+1:N) + alpha*C(I:M,I)*W(1:N-1)^H * ALPHA = -(T( I, 1 )) DO J = 1, N-I A( I, I+J ) = A( I, I+J ) + ALPHA*(T( J, N )) END DO CALL SGER( P, N-I, ALPHA, B( 1, I ), 1, \$ T( 1, N ), 1, B( 1, I+1 ), LDB ) END IF END DO * DO I = 2, N * * T(1:I-1,I) := C(I:M,1:I-1)^H * (alpha * C(I:M,I)) * ALPHA = -T( I, 1 ) DO J = 1, I-1 T( J, I ) = ZERO END DO P = MIN( I-1, L ) MP = MIN( M-L+1, M ) NP = MIN( P+1, N ) * * Triangular part of B2 * DO J = 1, P T( J, I ) = ALPHA*B( M-L+J, I ) END DO CALL STRMV( 'U', 'T', 'N', P, B( MP, 1 ), LDB, \$ T( 1, I ), 1 ) * * Rectangular part of B2 * CALL SGEMV( 'T', L, I-1-P, ALPHA, B( MP, NP ), LDB, \$ B( MP, I ), 1, ZERO, T( NP, I ), 1 ) * * B1 * CALL SGEMV( 'T', M-L, I-1, ALPHA, B, LDB, B( 1, I ), 1, \$ ONE, T( 1, I ), 1 ) * * T(1:I-1,I) := T(1:I-1,1:I-1) * T(1:I-1,I) * CALL STRMV( 'U', 'N', 'N', I-1, T, LDT, T( 1, I ), 1 ) * * T(I,I) = tau(I) * T( I, I ) = T( I, 1 ) T( I, 1 ) = ZERO END DO * * End of STPQRT2 * END