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

diff --git a/vendor/gonum.org/v1/gonum/lapack/gonum/dgebak.go b/vendor/gonum.org/v1/gonum/lapack/gonum/dgebak.go
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+++ b/vendor/gonum.org/v1/gonum/lapack/gonum/dgebak.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/blas64"
+       "gonum.org/v1/gonum/lapack"
+)
+
+// Dgebak updates an n×m matrix V as
+//  V = P D V,        if side == lapack.RightEV,
+//  V = P D^{-1} V,   if side == lapack.LeftEV,
+// where P and D are n×n permutation and scaling matrices, respectively,
+// implicitly represented by job, scale, ilo and ihi as returned by Dgebal.
+//
+// Typically, columns of the matrix V contain the right or left (determined by
+// side) eigenvectors of the balanced matrix output by Dgebal, and Dgebak forms
+// the eigenvectors of the original matrix.
+//
+// Dgebak is an internal routine. It is exported for testing purposes.
+func (impl Implementation) Dgebak(job lapack.Job, side lapack.EVSide, n, ilo, ihi int, scale []float64, m int, v []float64, ldv int) {
+       switch job {
+       default:
+               panic(badJob)
+       case lapack.None, lapack.Permute, lapack.Scale, lapack.PermuteScale:
+       }
+       switch side {
+       default:
+               panic(badEVSide)
+       case lapack.LeftEV, lapack.RightEV:
+       }
+       checkMatrix(n, m, v, ldv)
+       switch {
+       case ilo < 0 || max(0, n-1) < ilo:
+               panic(badIlo)
+       case ihi < min(ilo, n-1) || n <= ihi:
+               panic(badIhi)
+       }
+
+       // Quick return if possible.
+       if n == 0 || m == 0 || job == lapack.None {
+               return
+       }
+
+       bi := blas64.Implementation()
+       if ilo != ihi && job != lapack.Permute {
+               // Backward balance.
+               if side == lapack.RightEV {
+                       for i := ilo; i <= ihi; i++ {
+                               bi.Dscal(m, scale[i], v[i*ldv:], 1)
+                       }
+               } else {
+                       for i := ilo; i <= ihi; i++ {
+                               bi.Dscal(m, 1/scale[i], v[i*ldv:], 1)
+                       }
+               }
+       }
+       if job == lapack.Scale {
+               return
+       }
+       // Backward permutation.
+       for i := ilo - 1; i >= 0; i-- {
+               k := int(scale[i])
+               if k == i {
+                       continue
+               }
+               bi.Dswap(m, v[i*ldv:], 1, v[k*ldv:], 1)
+       }
+       for i := ihi + 1; i < n; i++ {
+               k := int(scale[i])
+               if k == i {
+                       continue
+               }
+               bi.Dswap(m, v[i*ldv:], 1, v[k*ldv:], 1)
+       }
+}