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58 lines
1.4 KiB
Go
58 lines
1.4 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 native
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import (
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"gonum.org/v1/gonum/blas"
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"gonum.org/v1/gonum/blas/blas64"
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)
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// Dtrti2 computes the inverse of a triangular matrix, storing the result in place
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// into a. This is the BLAS level 2 version of the algorithm.
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//
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// Dtrti2 is an internal routine. It is exported for testing purposes.
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func (impl Implementation) Dtrti2(uplo blas.Uplo, diag blas.Diag, n int, a []float64, lda int) {
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checkMatrix(n, n, a, lda)
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if uplo != blas.Upper && uplo != blas.Lower {
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panic(badUplo)
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}
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if diag != blas.NonUnit && diag != blas.Unit {
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panic(badDiag)
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}
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bi := blas64.Implementation()
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nonUnit := diag == blas.NonUnit
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// TODO(btracey): Replace this with a row-major ordering.
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if uplo == blas.Upper {
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for j := 0; j < n; j++ {
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var ajj float64
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if nonUnit {
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ajj = 1 / a[j*lda+j]
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a[j*lda+j] = ajj
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ajj *= -1
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} else {
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ajj = -1
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}
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bi.Dtrmv(blas.Upper, blas.NoTrans, diag, j, a, lda, a[j:], lda)
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bi.Dscal(j, ajj, a[j:], lda)
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}
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return
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}
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for j := n - 1; j >= 0; j-- {
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var ajj float64
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if nonUnit {
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ajj = 1 / a[j*lda+j]
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a[j*lda+j] = ajj
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ajj *= -1
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} else {
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ajj = -1
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}
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if j < n-1 {
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bi.Dtrmv(blas.Lower, blas.NoTrans, diag, n-j-1, a[(j+1)*lda+j+1:], lda, a[(j+1)*lda+j:], lda)
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bi.Dscal(n-j-1, ajj, a[(j+1)*lda+j:], lda)
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}
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}
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}
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