mirror of https://github.com/k3s-io/k3s
370 lines
9.2 KiB
Go
370 lines
9.2 KiB
Go
// Copyright ©2015 The Gonum Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package gonum
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import (
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"math"
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"gonum.org/v1/gonum/lapack"
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)
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// Dlasq2 computes all the eigenvalues of the symmetric positive
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// definite tridiagonal matrix associated with the qd array Z. Eigevalues
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// are computed to high relative accuracy avoiding denormalization, underflow
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// and overflow.
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//
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// To see the relation of Z to the tridiagonal matrix, let L be a
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// unit lower bidiagonal matrix with sub-diagonals Z(2,4,6,,..) and
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// let U be an upper bidiagonal matrix with 1's above and diagonal
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// Z(1,3,5,,..). The tridiagonal is L*U or, if you prefer, the
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// symmetric tridiagonal to which it is similar.
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//
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// info returns a status error. The return codes mean as follows:
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// 0: The algorithm completed successfully.
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// 1: A split was marked by a positive value in e.
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// 2: Current block of Z not diagonalized after 100*n iterations (in inner
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// while loop). On exit Z holds a qd array with the same eigenvalues as
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// the given Z.
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// 3: Termination criterion of outer while loop not met (program created more
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// than N unreduced blocks).
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//
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// z must have length at least 4*n, and must not contain any negative elements.
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// Dlasq2 will panic otherwise.
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//
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// Dlasq2 is an internal routine. It is exported for testing purposes.
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func (impl Implementation) Dlasq2(n int, z []float64) (info int) {
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if n < 0 {
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panic(nLT0)
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}
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if n == 0 {
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return info
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}
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if len(z) < 4*n {
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panic(shortZ)
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}
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if n == 1 {
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if z[0] < 0 {
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panic(negZ)
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}
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return info
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}
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const cbias = 1.5
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eps := dlamchP
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safmin := dlamchS
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tol := eps * 100
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tol2 := tol * tol
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if n == 2 {
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if z[1] < 0 || z[2] < 0 {
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panic(negZ)
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} else if z[2] > z[0] {
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z[0], z[2] = z[2], z[0]
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}
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z[4] = z[0] + z[1] + z[2]
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if z[1] > z[2]*tol2 {
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t := 0.5 * (z[0] - z[2] + z[1])
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s := z[2] * (z[1] / t)
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if s <= t {
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s = z[2] * (z[1] / (t * (1 + math.Sqrt(1+s/t))))
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} else {
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s = z[2] * (z[1] / (t + math.Sqrt(t)*math.Sqrt(t+s)))
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}
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t = z[0] + s + z[1]
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z[2] *= z[0] / t
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z[0] = t
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}
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z[1] = z[2]
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z[5] = z[1] + z[0]
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return info
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}
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// Check for negative data and compute sums of q's and e's.
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z[2*n-1] = 0
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emin := z[1]
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var d, e, qmax float64
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var i1, n1 int
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for k := 0; k < 2*(n-1); k += 2 {
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if z[k] < 0 || z[k+1] < 0 {
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panic(negZ)
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}
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d += z[k]
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e += z[k+1]
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qmax = math.Max(qmax, z[k])
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emin = math.Min(emin, z[k+1])
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}
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if z[2*(n-1)] < 0 {
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panic(negZ)
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}
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d += z[2*(n-1)]
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// Check for diagonality.
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if e == 0 {
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for k := 1; k < n; k++ {
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z[k] = z[2*k]
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}
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impl.Dlasrt(lapack.SortDecreasing, n, z)
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z[2*(n-1)] = d
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return info
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}
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trace := d + e
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// Check for zero data.
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if trace == 0 {
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z[2*(n-1)] = 0
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return info
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}
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// Rearrange data for locality: Z=(q1,qq1,e1,ee1,q2,qq2,e2,ee2,...).
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for k := 2 * n; k >= 2; k -= 2 {
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z[2*k-1] = 0
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z[2*k-2] = z[k-1]
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z[2*k-3] = 0
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z[2*k-4] = z[k-2]
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}
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i0 := 0
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n0 := n - 1
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// Reverse the qd-array, if warranted.
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// z[4*i0-3] --> z[4*(i0+1)-3-1] --> z[4*i0]
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if cbias*z[4*i0] < z[4*n0] {
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ipn4Out := 4 * (i0 + n0 + 2)
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for i4loop := 4 * (i0 + 1); i4loop <= 2*(i0+n0+1); i4loop += 4 {
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i4 := i4loop - 1
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ipn4 := ipn4Out - 1
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z[i4-3], z[ipn4-i4-4] = z[ipn4-i4-4], z[i4-3]
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z[i4-1], z[ipn4-i4-6] = z[ipn4-i4-6], z[i4-1]
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}
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}
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// Initial split checking via dqd and Li's test.
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pp := 0
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for k := 0; k < 2; k++ {
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d = z[4*n0+pp]
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for i4loop := 4*n0 + pp; i4loop >= 4*(i0+1)+pp; i4loop -= 4 {
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i4 := i4loop - 1
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if z[i4-1] <= tol2*d {
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z[i4-1] = math.Copysign(0, -1)
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d = z[i4-3]
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} else {
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d = z[i4-3] * (d / (d + z[i4-1]))
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}
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}
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// dqd maps Z to ZZ plus Li's test.
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emin = z[4*(i0+1)+pp]
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d = z[4*i0+pp]
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for i4loop := 4*(i0+1) + pp; i4loop <= 4*n0+pp; i4loop += 4 {
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i4 := i4loop - 1
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z[i4-2*pp-2] = d + z[i4-1]
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if z[i4-1] <= tol2*d {
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z[i4-1] = math.Copysign(0, -1)
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z[i4-2*pp-2] = d
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z[i4-2*pp] = 0
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d = z[i4+1]
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} else if safmin*z[i4+1] < z[i4-2*pp-2] && safmin*z[i4-2*pp-2] < z[i4+1] {
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tmp := z[i4+1] / z[i4-2*pp-2]
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z[i4-2*pp] = z[i4-1] * tmp
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d *= tmp
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} else {
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z[i4-2*pp] = z[i4+1] * (z[i4-1] / z[i4-2*pp-2])
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d = z[i4+1] * (d / z[i4-2*pp-2])
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}
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emin = math.Min(emin, z[i4-2*pp])
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}
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z[4*(n0+1)-pp-3] = d
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// Now find qmax.
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qmax = z[4*(i0+1)-pp-3]
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for i4loop := 4*(i0+1) - pp + 2; i4loop <= 4*(n0+1)+pp-2; i4loop += 4 {
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i4 := i4loop - 1
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qmax = math.Max(qmax, z[i4])
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}
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// Prepare for the next iteration on K.
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pp = 1 - pp
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}
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// Initialise variables to pass to DLASQ3.
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var ttype int
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var dmin1, dmin2, dn, dn1, dn2, g, tau float64
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var tempq float64
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iter := 2
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var nFail int
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nDiv := 2 * (n0 - i0)
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var i4 int
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outer:
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for iwhila := 1; iwhila <= n+1; iwhila++ {
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// Test for completion.
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if n0 < 0 {
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// Move q's to the front.
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for k := 1; k < n; k++ {
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z[k] = z[4*k]
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}
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// Sort and compute sum of eigenvalues.
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impl.Dlasrt(lapack.SortDecreasing, n, z)
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e = 0
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for k := n - 1; k >= 0; k-- {
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e += z[k]
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}
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// Store trace, sum(eigenvalues) and information on performance.
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z[2*n] = trace
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z[2*n+1] = e
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z[2*n+2] = float64(iter)
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z[2*n+3] = float64(nDiv) / float64(n*n)
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z[2*n+4] = 100 * float64(nFail) / float64(iter)
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return info
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}
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// While array unfinished do
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// e[n0] holds the value of sigma when submatrix in i0:n0
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// splits from the rest of the array, but is negated.
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var desig float64
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var sigma float64
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if n0 != n-1 {
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sigma = -z[4*(n0+1)-2]
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}
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if sigma < 0 {
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info = 1
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return info
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}
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// Find last unreduced submatrix's top index i0, find qmax and
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// emin. Find Gershgorin-type bound if Q's much greater than E's.
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var emax float64
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if n0 > i0 {
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emin = math.Abs(z[4*(n0+1)-6])
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} else {
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emin = 0
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}
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qmin := z[4*(n0+1)-4]
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qmax = qmin
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zSmall := false
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for i4loop := 4 * (n0 + 1); i4loop >= 8; i4loop -= 4 {
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i4 = i4loop - 1
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if z[i4-5] <= 0 {
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zSmall = true
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break
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}
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if qmin >= 4*emax {
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qmin = math.Min(qmin, z[i4-3])
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emax = math.Max(emax, z[i4-5])
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}
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qmax = math.Max(qmax, z[i4-7]+z[i4-5])
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emin = math.Min(emin, z[i4-5])
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}
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if !zSmall {
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i4 = 3
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}
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i0 = (i4+1)/4 - 1
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pp = 0
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if n0-i0 > 1 {
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dee := z[4*i0]
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deemin := dee
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kmin := i0
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for i4loop := 4*(i0+1) + 1; i4loop <= 4*(n0+1)-3; i4loop += 4 {
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i4 := i4loop - 1
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dee = z[i4] * (dee / (dee + z[i4-2]))
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if dee <= deemin {
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deemin = dee
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kmin = (i4+4)/4 - 1
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}
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}
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if (kmin-i0)*2 < n0-kmin && deemin <= 0.5*z[4*n0] {
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ipn4Out := 4 * (i0 + n0 + 2)
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pp = 2
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for i4loop := 4 * (i0 + 1); i4loop <= 2*(i0+n0+1); i4loop += 4 {
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i4 := i4loop - 1
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ipn4 := ipn4Out - 1
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z[i4-3], z[ipn4-i4-4] = z[ipn4-i4-4], z[i4-3]
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z[i4-2], z[ipn4-i4-3] = z[ipn4-i4-3], z[i4-2]
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z[i4-1], z[ipn4-i4-6] = z[ipn4-i4-6], z[i4-1]
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z[i4], z[ipn4-i4-5] = z[ipn4-i4-5], z[i4]
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}
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}
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}
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// Put -(initial shift) into DMIN.
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dmin := -math.Max(0, qmin-2*math.Sqrt(qmin)*math.Sqrt(emax))
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// Now i0:n0 is unreduced.
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// PP = 0 for ping, PP = 1 for pong.
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// PP = 2 indicates that flipping was applied to the Z array and
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// and that the tests for deflation upon entry in Dlasq3
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// should not be performed.
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nbig := 100 * (n0 - i0 + 1)
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for iwhilb := 0; iwhilb < nbig; iwhilb++ {
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if i0 > n0 {
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continue outer
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}
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// While submatrix unfinished take a good dqds step.
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i0, n0, pp, dmin, sigma, desig, qmax, nFail, iter, nDiv, ttype, dmin1, dmin2, dn, dn1, dn2, g, tau =
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impl.Dlasq3(i0, n0, z, pp, dmin, sigma, desig, qmax, nFail, iter, nDiv, ttype, dmin1, dmin2, dn, dn1, dn2, g, tau)
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pp = 1 - pp
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// When emin is very small check for splits.
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if pp == 0 && n0-i0 >= 3 {
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if z[4*(n0+1)-1] <= tol2*qmax || z[4*(n0+1)-2] <= tol2*sigma {
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splt := i0 - 1
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qmax = z[4*i0]
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emin = z[4*(i0+1)-2]
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oldemn := z[4*(i0+1)-1]
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for i4loop := 4 * (i0 + 1); i4loop <= 4*(n0-2); i4loop += 4 {
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i4 := i4loop - 1
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if z[i4] <= tol2*z[i4-3] || z[i4-1] <= tol2*sigma {
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z[i4-1] = -sigma
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splt = i4 / 4
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qmax = 0
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emin = z[i4+3]
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oldemn = z[i4+4]
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} else {
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qmax = math.Max(qmax, z[i4+1])
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emin = math.Min(emin, z[i4-1])
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oldemn = math.Min(oldemn, z[i4])
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}
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}
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z[4*(n0+1)-2] = emin
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z[4*(n0+1)-1] = oldemn
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i0 = splt + 1
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}
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}
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}
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// Maximum number of iterations exceeded, restore the shift
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// sigma and place the new d's and e's in a qd array.
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// This might need to be done for several blocks.
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info = 2
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i1 = i0
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for {
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tempq = z[4*i0]
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z[4*i0] += sigma
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for k := i0 + 1; k <= n0; k++ {
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tempe := z[4*(k+1)-6]
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z[4*(k+1)-6] *= tempq / z[4*(k+1)-8]
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tempq = z[4*k]
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z[4*k] += sigma + tempe - z[4*(k+1)-6]
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}
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// Prepare to do this on the previous block if there is one.
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if i1 <= 0 {
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break
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}
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n1 = i1 - 1
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for i1 >= 1 && z[4*(i1+1)-6] >= 0 {
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i1 -= 1
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}
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sigma = -z[4*(n1+1)-2]
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}
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for k := 0; k < n; k++ {
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z[2*k] = z[4*k]
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// Only the block 1..N0 is unfinished. The rest of the e's
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// must be essentially zero, although sometimes other data
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// has been stored in them.
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if k < n0 {
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z[2*(k+1)-1] = z[4*(k+1)-1]
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} else {
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z[2*(k+1)] = 0
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}
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}
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return info
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}
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info = 3
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return info
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}
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