--- /dev/null
+// Copyright ©2016 The Gonum Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package gonum
+
+import "gonum.org/v1/gonum/blas"
+
+// Dormhr multiplies an m×n general matrix C with an nq×nq orthogonal matrix Q
+// Q * C, if side == blas.Left and trans == blas.NoTrans,
+// Q^T * C, if side == blas.Left and trans == blas.Trans,
+// C * Q, if side == blas.Right and trans == blas.NoTrans,
+// C * Q^T, if side == blas.Right and trans == blas.Trans,
+// where nq == m if side == blas.Left and nq == n if side == blas.Right.
+//
+// Q is defined implicitly as the product of ihi-ilo elementary reflectors, as
+// returned by Dgehrd:
+// Q = H_{ilo} H_{ilo+1} ... H_{ihi-1}.
+// Q is equal to the identity matrix except in the submatrix
+// Q[ilo+1:ihi+1,ilo+1:ihi+1].
+//
+// ilo and ihi must have the same values as in the previous call of Dgehrd. It
+// must hold that
+// 0 <= ilo <= ihi < m, if m > 0 and side == blas.Left,
+// ilo = 0 and ihi = -1, if m = 0 and side == blas.Left,
+// 0 <= ilo <= ihi < n, if n > 0 and side == blas.Right,
+// ilo = 0 and ihi = -1, if n = 0 and side == blas.Right.
+//
+// a and lda represent an m×m matrix if side == blas.Left and an n×n matrix if
+// side == blas.Right. The matrix contains vectors which define the elementary
+// reflectors, as returned by Dgehrd.
+//
+// tau contains the scalar factors of the elementary reflectors, as returned by
+// Dgehrd. tau must have length m-1 if side == blas.Left and n-1 if side ==
+// blas.Right.
+//
+// c and ldc represent the m×n matrix C. On return, c is overwritten by the
+// product with Q.
+//
+// work must have length at least max(1,lwork), and lwork must be at least
+// max(1,n), if side == blas.Left, and max(1,m), if side == blas.Right. For
+// optimum performance lwork should be at least n*nb if side == blas.Left and
+// m*nb if side == blas.Right, where nb is the optimal block size. On return,
+// work[0] will contain the optimal value of lwork.
+//
+// If lwork == -1, instead of performing Dormhr, only the optimal value of lwork
+// will be stored in work[0].
+//
+// If any requirement on input sizes is not met, Dormhr will panic.
+//
+// Dormhr is an internal routine. It is exported for testing purposes.
+func (impl Implementation) Dormhr(side blas.Side, trans blas.Transpose, m, n, ilo, ihi int, a []float64, lda int, tau, c []float64, ldc int, work []float64, lwork int) {
+ var (
+ nq int // The order of Q.
+ nw int // The minimum length of work.
+ )
+ switch side {
+ case blas.Left:
+ nq = m
+ nw = n
+ case blas.Right:
+ nq = n
+ nw = m
+ default:
+ panic(badSide)
+ }
+ switch {
+ case trans != blas.NoTrans && trans != blas.Trans:
+ panic(badTrans)
+ case ilo < 0 || max(1, nq) <= ilo:
+ panic(badIlo)
+ case ihi < min(ilo, nq-1) || nq <= ihi:
+ panic(badIhi)
+ case lwork < max(1, nw) && lwork != -1:
+ panic(badWork)
+ case len(work) < max(1, lwork):
+ panic(shortWork)
+ }
+ if lwork != -1 {
+ checkMatrix(m, n, c, ldc)
+ checkMatrix(nq, nq, a, lda)
+ if len(tau) != nq-1 && nq > 0 {
+ panic(badTau)
+ }
+
+ }
+
+ nh := ihi - ilo
+ var nb int
+ if side == blas.Left {
+ opts := "LN"
+ if trans == blas.Trans {
+ opts = "LT"
+ }
+ nb = impl.Ilaenv(1, "DORMQR", opts, nh, n, nh, -1)
+ } else {
+ opts := "RN"
+ if trans == blas.Trans {
+ opts = "RT"
+ }
+ nb = impl.Ilaenv(1, "DORMQR", opts, m, nh, nh, -1)
+ }
+ lwkopt := max(1, nw) * nb
+ if lwork == -1 {
+ work[0] = float64(lwkopt)
+ return
+ }
+
+ if m == 0 || n == 0 || nh == 0 {
+ work[0] = 1
+ return
+ }
+ if side == blas.Left {
+ impl.Dormqr(side, trans, nh, n, nh, a[(ilo+1)*lda+ilo:], lda,
+ tau[ilo:ihi], c[(ilo+1)*ldc:], ldc, work, lwork)
+ } else {
+ impl.Dormqr(side, trans, m, nh, nh, a[(ilo+1)*lda+ilo:], lda,
+ tau[ilo:ihi], c[ilo+1:], ldc, work, lwork)
+ }
+ work[0] = float64(lwkopt)
+}
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