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123 lines
2.6 KiB
Go
123 lines
2.6 KiB
Go
package native
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import (
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"math"
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"github.com/gonum/blas/blas64"
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)
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// Dlacn2 estimates the 1-norm of an n×n matrix A using sequential updates with
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// matrix-vector products provided externally.
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//
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// Dlacn2 is called sequentially. In between calls, x should be overwritten by
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// A * X if kase == 1
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// A^T * X if kase == 2
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// all other prameters should be unchanged during sequential calls, and the updated
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// values of est and kase should be used. On the final return (when kase is returned
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// as 0), V = A * W, where est = norm(V) / norm(W).
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//
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// isign, v, and x must all have length n and will panic otherwise. isave is used
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// for temporary storage.
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func (impl Implementation) Dlacn2(n int, v, x []float64, isgn []int, est float64, kase int, isave *[3]int) (float64, int) {
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checkVector(n, x, 1)
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checkVector(n, v, 1)
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if len(isgn) < n {
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panic("lapack: insufficient isgn length")
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}
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if isave[0] < 0 || isave[0] > 5 {
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panic("lapack: bad isave value")
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}
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if isave[0] == 0 && kase != 0 {
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panic("lapack: bad isave value")
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}
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itmax := 5
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bi := blas64.Implementation()
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if kase == 0 {
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for i := 0; i < n; i++ {
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x[i] = 1 / float64(n)
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}
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kase = 1
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isave[0] = 1
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return est, kase
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}
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switch isave[0] {
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default:
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panic("unreachable")
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case 1:
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if n == 1 {
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v[0] = x[0]
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est = math.Abs(v[0])
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kase = 0
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return est, kase
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}
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est = bi.Dasum(n, x, 1)
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for i := 0; i < n; i++ {
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x[i] = math.Copysign(1, x[i])
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isgn[i] = int(x[i])
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}
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kase = 2
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isave[0] = 2
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return est, kase
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case 2:
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isave[1] = bi.Idamax(n, x, 1)
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isave[2] = 2
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for i := 0; i < n; i++ {
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x[i] = 0
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}
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x[isave[1]] = 1
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kase = 1
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isave[0] = 3
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return est, kase
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case 3:
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bi.Dcopy(n, x, 1, v, 1)
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estold := est
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est = bi.Dasum(n, v, 1)
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sameSigns := true
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for i := 0; i < n; i++ {
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if int(math.Copysign(1, x[i])) != isgn[i] {
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sameSigns = false
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break
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}
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}
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if !sameSigns && est > estold {
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for i := 0; i < n; i++ {
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x[i] = math.Copysign(1, x[i])
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isgn[i] = int(x[i])
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}
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kase = 2
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isave[0] = 4
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return est, kase
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}
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case 4:
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jlast := isave[1]
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isave[1] = bi.Idamax(n, x, 1)
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if x[jlast] != math.Abs(x[isave[1]]) && isave[2] < itmax {
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isave[2] += 1
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for i := 0; i < n; i++ {
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x[i] = 0
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}
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x[isave[1]] = 1
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kase = 1
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isave[0] = 3
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return est, kase
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}
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case 5:
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tmp := 2 * (bi.Dasum(n, x, 1)) / float64(3*n)
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if tmp > est {
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bi.Dcopy(n, x, 1, v, 1)
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est = tmp
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}
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kase = 0
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return est, kase
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}
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// Iteration complete. Final stage
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altsgn := 1.0
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for i := 0; i < n; i++ {
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x[i] = altsgn * (1 + float64(i)/float64(n-1))
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altsgn *= -1
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}
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kase = 1
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isave[0] = 5
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return est, kase
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}
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