diff --git a/native/dlaqr1.go b/native/dlaqr1.go new file mode 100644 index 00000000..4d482a5d --- /dev/null +++ b/native/dlaqr1.go @@ -0,0 +1,57 @@ +// 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 native + +import "math" + +// Dlaqr1 sets v to a scalar multiple of the first column of the product +// (H - (sr1 + i*si1)*I)*(H - (sr2 + i*si2)*I) +// where H is a 2×2 or 3×3 matrix, I is the identity matrix of the same size, +// and i is the imaginary unit. Scaling is done to avoid overflows and most +// underflows. +// +// n is the order of H and must be either 2 or 3. It must hold that either sr1 = +// sr2 and si1 = -si2, or si1 = si2 = 0. The length of v must be equal to n. If +// any of these conditions is not met, Dlaqr1 will panic. +// +// Dlaqr1 is an internal routine. It is exported for testing purposes. +func (impl Implementation) Dlaqr1(n int, h []float64, ldh int, sr1, si1, sr2, si2 float64, v []float64) { + if n != 2 && n != 3 { + panic(badDims) + } + checkMatrix(n, n, h, ldh) + if len(v) != n { + panic(badSlice) + } + if !((sr1 == sr2 && si1 == -si2) || (si1 == 0 && si2 == 0)) { + panic(badShifts) + } + + if n == 2 { + s := math.Abs(h[0]-sr2) + math.Abs(si2) + math.Abs(h[ldh]) + if s == 0 { + v[0] = 0 + v[1] = 0 + } else { + h21s := h[ldh] / s + v[0] = h21s*h[1] + (h[0]-sr1)*((h[0]-sr2)/s) - si1*(si2/s) + v[1] = h21s * (h[0] + h[ldh+1] - sr1 - sr2) + } + return + } + + s := math.Abs(h[0]-sr2) + math.Abs(si2) + math.Abs(h[ldh]) + math.Abs(h[2*ldh]) + if s == 0 { + v[0] = 0 + v[1] = 0 + v[2] = 0 + } else { + h21s := h[ldh] / s + h31s := h[2*ldh] / s + v[0] = (h[0]-sr1)*((h[0]-sr2)/s) - si1*(si2/s) + h[1]*h21s + h[2]*h31s + v[1] = h21s*(h[0]+h[ldh+1]-sr1-sr2) + h[ldh+2]*h31s + v[2] = h31s*(h[0]+h[2*ldh+2]-sr1-sr2) + h21s*h[2*ldh+1] + } +} diff --git a/native/general.go b/native/general.go index a3bd2ded..2d20af87 100644 --- a/native/general.go +++ b/native/general.go @@ -32,6 +32,7 @@ const ( badNorm = "lapack: bad norm" badPivot = "lapack: bad pivot" badS = "lapack: s has insufficient length" + badShifts = "lapack: bad shifts" badSide = "lapack: bad side" badSlice = "lapack: bad input slice length" badStore = "lapack: bad store"