#include "blaswrap.h" #include "f2c.h" /* Subroutine */ int dlarzt_(char *direct, char *storev, integer *n, integer * k, doublereal *v, integer *ldv, doublereal *tau, doublereal *t, integer *ldt) { /* -- LAPACK routine (version 3.1) -- Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. November 2006 Purpose ======= DLARZT forms the triangular factor T of a real block reflector H of order > n, which is defined as a product of k elementary reflectors. If DIRECT = 'F', H = H(1) H(2) . . . H(k) and T is upper triangular; If DIRECT = 'B', H = H(k) . . . H(2) H(1) and T is lower triangular. If STOREV = 'C', the vector which defines the elementary reflector H(i) is stored in the i-th column of the array V, and H = I - V * T * V' If STOREV = 'R', the vector which defines the elementary reflector H(i) is stored in the i-th row of the array V, and H = I - V' * T * V Currently, only STOREV = 'R' and DIRECT = 'B' are supported. Arguments ========= DIRECT (input) CHARACTER*1 Specifies the order in which the elementary reflectors are multiplied to form the block reflector: = 'F': H = H(1) H(2) . . . H(k) (Forward, not supported yet) = 'B': H = H(k) . . . H(2) H(1) (Backward) STOREV (input) CHARACTER*1 Specifies how the vectors which define the elementary reflectors are stored (see also Further Details): = 'C': columnwise (not supported yet) = 'R': rowwise N (input) INTEGER The order of the block reflector H. N >= 0. K (input) INTEGER The order of the triangular factor T (= the number of elementary reflectors). K >= 1. V (input/output) DOUBLE PRECISION array, dimension (LDV,K) if STOREV = 'C' (LDV,N) if STOREV = 'R' The matrix V. See further details. LDV (input) INTEGER The leading dimension of the array V. If STOREV = 'C', LDV >= max(1,N); if STOREV = 'R', LDV >= K. TAU (input) DOUBLE PRECISION array, dimension (K) TAU(i) must contain the scalar factor of the elementary reflector H(i). T (output) DOUBLE PRECISION array, dimension (LDT,K) The k by k triangular factor T of the block reflector. If DIRECT = 'F', T is upper triangular; if DIRECT = 'B', T is lower triangular. The rest of the array is not used. LDT (input) INTEGER The leading dimension of the array T. LDT >= K. Further Details =============== Based on contributions by A. Petitet, Computer Science Dept., Univ. of Tenn., Knoxville, USA The shape of the matrix V and the storage of the vectors which define the H(i) is best illustrated by the following example with n = 5 and k = 3. The elements equal to 1 are not stored; the corresponding array elements are modified but restored on exit. The rest of the array is not used. DIRECT = 'F' and STOREV = 'C': DIRECT = 'F' and STOREV = 'R': ______V_____ ( v1 v2 v3 ) / \ ( v1 v2 v3 ) ( v1 v1 v1 v1 v1 . . . . 1 ) V = ( v1 v2 v3 ) ( v2 v2 v2 v2 v2 . . . 1 ) ( v1 v2 v3 ) ( v3 v3 v3 v3 v3 . . 1 ) ( v1 v2 v3 ) . . . . . . 1 . . 1 . 1 DIRECT = 'B' and STOREV = 'C': DIRECT = 'B' and STOREV = 'R': ______V_____ 1 / \ . 1 ( 1 . . . . v1 v1 v1 v1 v1 ) . . 1 ( . 1 . . . v2 v2 v2 v2 v2 ) . . . ( . . 1 . . v3 v3 v3 v3 v3 ) . . . ( v1 v2 v3 ) ( v1 v2 v3 ) V = ( v1 v2 v3 ) ( v1 v2 v3 ) ( v1 v2 v3 ) ===================================================================== Check for currently supported options Parameter adjustments */ /* Table of constant values */ static doublereal c_b8 = 0.; static integer c__1 = 1; /* System generated locals */ integer t_dim1, t_offset, v_dim1, v_offset, i__1; doublereal d__1; /* Local variables */ static integer i__, j, info; extern logical lsame_(char *, char *); extern /* Subroutine */ int dgemv_(char *, integer *, integer *, doublereal *, doublereal *, integer *, doublereal *, integer *, doublereal *, doublereal *, integer *), dtrmv_(char *, char *, char *, integer *, doublereal *, integer *, doublereal *, integer *), xerbla_(char *, integer *); v_dim1 = *ldv; v_offset = 1 + v_dim1; v -= v_offset; --tau; t_dim1 = *ldt; t_offset = 1 + t_dim1; t -= t_offset; /* Function Body */ info = 0; if (! lsame_(direct, "B")) { info = -1; } else if (! lsame_(storev, "R")) { info = -2; } if (info != 0) { i__1 = -info; xerbla_("DLARZT", &i__1); return 0; } for (i__ = *k; i__ >= 1; --i__) { if (tau[i__] == 0.) { /* H(i) = I */ i__1 = *k; for (j = i__; j <= i__1; ++j) { t[j + i__ * t_dim1] = 0.; /* L10: */ } } else { /* general case */ if (i__ < *k) { /* T(i+1:k,i) = - tau(i) * V(i+1:k,1:n) * V(i,1:n)' */ i__1 = *k - i__; d__1 = -tau[i__]; dgemv_("No transpose", &i__1, n, &d__1, &v[i__ + 1 + v_dim1], ldv, &v[i__ + v_dim1], ldv, &c_b8, &t[i__ + 1 + i__ * t_dim1], &c__1); /* T(i+1:k,i) = T(i+1:k,i+1:k) * T(i+1:k,i) */ i__1 = *k - i__; dtrmv_("Lower", "No transpose", "Non-unit", &i__1, &t[i__ + 1 + (i__ + 1) * t_dim1], ldt, &t[i__ + 1 + i__ * t_dim1] , &c__1); } t[i__ + i__ * t_dim1] = tau[i__]; } /* L20: */ } return 0; /* End of DLARZT */ } /* dlarzt_ */