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

diff --git a/vendor/gonum.org/v1/gonum/lapack/gonum/dlapll.go b/vendor/gonum.org/v1/gonum/lapack/gonum/dlapll.go
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+// Copyright ©2017 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"
+
+// Dlapll returns the smallest singular value of the n×2 matrix A = [ x y ].
+// The function first computes the QR factorization of A = Q*R, and then computes
+// the SVD of the 2-by-2 upper triangular matrix r.
+//
+// The contents of x and y are overwritten during the call.
+//
+// Dlapll is an internal routine. It is exported for testing purposes.
+func (impl Implementation) Dlapll(n int, x []float64, incX int, y []float64, incY int) float64 {
+       checkVector(n, x, incX)
+       checkVector(n, y, incY)
+
+       if n <= 1 {
+               return 0
+       }
+
+       // Compute the QR factorization of the N-by-2 matrix [ X Y ].
+       a00, tau := impl.Dlarfg(n, x[0], x[incX:], incX)
+       x[0] = 1
+
+       bi := blas64.Implementation()
+       c := -tau * bi.Ddot(n, x, incX, y, incY)
+       bi.Daxpy(n, c, x, incX, y, incY)
+       a11, _ := impl.Dlarfg(n-1, y[incY], y[2*incY:], incY)
+
+       // Compute the SVD of 2-by-2 upper triangular matrix.
+       ssmin, _ := impl.Dlas2(a00, y[0], a11)
+       return ssmin
+}