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76 lines
1.7 KiB
Go
76 lines
1.7 KiB
Go
// Copyright ©2020 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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"gonum.org/v1/gonum/blas"
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"gonum.org/v1/gonum/blas/blas64"
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)
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// Dtbtrs solves a triangular system of the form
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// A * X = B if trans == blas.NoTrans
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// Aᵀ * X = B if trans == blas.Trans or blas.ConjTrans
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// where A is an n×n triangular band matrix with kd super- or subdiagonals, and
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// B is an n×nrhs matrix.
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//
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// Dtbtrs returns whether A is non-singular. If A is singular, no solution X is
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// computed.
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func (impl Implementation) Dtbtrs(uplo blas.Uplo, trans blas.Transpose, diag blas.Diag, n, kd, nrhs int, a []float64, lda int, b []float64, ldb int) (ok bool) {
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switch {
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case uplo != blas.Upper && uplo != blas.Lower:
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panic(badUplo)
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case trans != blas.NoTrans && trans != blas.Trans && trans != blas.ConjTrans:
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panic(badTrans)
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case diag != blas.NonUnit && diag != blas.Unit:
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panic(badDiag)
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case n < 0:
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panic(nLT0)
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case kd < 0:
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panic(kdLT0)
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case nrhs < 0:
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panic(nrhsLT0)
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case lda < kd+1:
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panic(badLdA)
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case ldb < max(1, nrhs):
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panic(badLdB)
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}
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// Quick return if possible.
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if n == 0 {
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return true
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}
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switch {
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case len(a) < (n-1)*lda+kd+1:
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panic(shortA)
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case len(b) < (n-1)*ldb+nrhs:
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panic(shortB)
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}
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// Check for singularity.
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if diag == blas.NonUnit {
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if uplo == blas.Upper {
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for i := 0; i < n; i++ {
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if a[i*lda] == 0 {
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return false
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}
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}
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} else {
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for i := 0; i < n; i++ {
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if a[i*lda+kd] == 0 {
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return false
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}
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}
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}
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}
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// Solve A * X = B or Aᵀ * X = B.
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bi := blas64.Implementation()
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for j := 0; j < nrhs; j++ {
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bi.Dtbsv(uplo, trans, diag, n, kd, a, lda, b[j:], ldb)
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}
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return true
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}
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