Hulk did something

[bytom/vapor.git] / vendor / gonum.org / v1 / gonum / lapack / gonum / dorgtr.go

diff --git a/vendor/gonum.org/v1/gonum/lapack/gonum/dorgtr.go b/vendor/gonum.org/v1/gonum/lapack/gonum/dorgtr.go
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+// 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"
+
+// Dorgtr generates a real orthogonal matrix Q which is defined as the product
+// of n-1 elementary reflectors of order n as returned by Dsytrd.
+//
+// The construction of Q depends on the value of uplo:
+//  Q = H_{n-1} * ... * H_1 * H_0  if uplo == blas.Upper
+//  Q = H_0 * H_1 * ... * H_{n-1}  if uplo == blas.Lower
+// where H_i is constructed from the elementary reflectors as computed by Dsytrd.
+// See the documentation for Dsytrd for more information.
+//
+// tau must have length at least n-1, and Dorgtr will panic otherwise.
+//
+// work is temporary storage, and lwork specifies the usable memory length. At
+// minimum, lwork >= max(1,n-1), and Dorgtr will panic otherwise. The amount of blocking
+// is limited by the usable length.
+// If lwork == -1, instead of computing Dorgtr the optimal work length is stored
+// into work[0].
+//
+// Dorgtr is an internal routine. It is exported for testing purposes.
+func (impl Implementation) Dorgtr(uplo blas.Uplo, n int, a []float64, lda int, tau, work []float64, lwork int) {
+       checkMatrix(n, n, a, lda)
+       if len(tau) < n-1 {
+               panic(badTau)
+       }
+       if len(work) < lwork {
+               panic(badWork)
+       }
+       if lwork < n-1 && lwork != -1 {
+               panic(badWork)
+       }
+       upper := uplo == blas.Upper
+       if !upper && uplo != blas.Lower {
+               panic(badUplo)
+       }
+
+       if n == 0 {
+               work[0] = 1
+               return
+       }
+
+       var nb int
+       if upper {
+               nb = impl.Ilaenv(1, "DORGQL", " ", n-1, n-1, n-1, -1)
+       } else {
+               nb = impl.Ilaenv(1, "DORGQR", " ", n-1, n-1, n-1, -1)
+       }
+       lworkopt := max(1, n-1) * nb
+       if lwork == -1 {
+               work[0] = float64(lworkopt)
+               return
+       }
+
+       if upper {
+               // Q was determined by a call to Dsytrd with uplo == blas.Upper.
+               // Shift the vectors which define the elementary reflectors one column
+               // to the left, and set the last row and column of Q to those of the unit
+               // matrix.
+               for j := 0; j < n-1; j++ {
+                       for i := 0; i < j; i++ {
+                               a[i*lda+j] = a[i*lda+j+1]
+                       }
+                       a[(n-1)*lda+j] = 0
+               }
+               for i := 0; i < n-1; i++ {
+                       a[i*lda+n-1] = 0
+               }
+               a[(n-1)*lda+n-1] = 1
+
+               // Generate Q[0:n-1, 0:n-1].
+               impl.Dorgql(n-1, n-1, n-1, a, lda, tau, work, lwork)
+       } else {
+               // Q was determined by a call to Dsytrd with uplo == blas.Upper.
+               // Shift the vectors which define the elementary reflectors one column
+               // to the right, and set the first row and column of Q to those of the unit
+               // matrix.
+               for j := n - 1; j > 0; j-- {
+                       a[j] = 0
+                       for i := j + 1; i < n; i++ {
+                               a[i*lda+j] = a[i*lda+j-1]
+                       }
+               }
+               a[0] = 1
+               for i := 1; i < n; i++ {
+                       a[i*lda] = 0
+               }
+               if n > 1 {
+                       // Generate Q[1:n, 1:n].
+                       impl.Dorgqr(n-1, n-1, n-1, a[lda+1:], lda, tau, work, lwork)
+               }
+       }
+       work[0] = float64(lworkopt)
+}