github.com/gopherd/gonum@v0.0.4/lapack/gonum/dtbtrs.go (about)

     1  // Copyright ©2020 The Gonum Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package gonum
     6  
     7  import (
     8  	"github.com/gopherd/gonum/blas"
     9  	"github.com/gopherd/gonum/blas/blas64"
    10  )
    11  
    12  // Dtbtrs solves a triangular system of the form
    13  //  A * X = B   if trans == blas.NoTrans
    14  //  Aᵀ * X = B  if trans == blas.Trans or blas.ConjTrans
    15  // where A is an n×n triangular band matrix with kd super- or subdiagonals, and
    16  // B is an n×nrhs matrix.
    17  //
    18  // Dtbtrs returns whether A is non-singular. If A is singular, no solution X is
    19  // computed.
    20  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) {
    21  	switch {
    22  	case uplo != blas.Upper && uplo != blas.Lower:
    23  		panic(badUplo)
    24  	case trans != blas.NoTrans && trans != blas.Trans && trans != blas.ConjTrans:
    25  		panic(badTrans)
    26  	case diag != blas.NonUnit && diag != blas.Unit:
    27  		panic(badDiag)
    28  	case n < 0:
    29  		panic(nLT0)
    30  	case kd < 0:
    31  		panic(kdLT0)
    32  	case nrhs < 0:
    33  		panic(nrhsLT0)
    34  	case lda < kd+1:
    35  		panic(badLdA)
    36  	case ldb < max(1, nrhs):
    37  		panic(badLdB)
    38  	}
    39  
    40  	// Quick return if possible.
    41  	if n == 0 {
    42  		return true
    43  	}
    44  
    45  	switch {
    46  	case len(a) < (n-1)*lda+kd+1:
    47  		panic(shortA)
    48  	case len(b) < (n-1)*ldb+nrhs:
    49  		panic(shortB)
    50  	}
    51  
    52  	// Check for singularity.
    53  	if diag == blas.NonUnit {
    54  		if uplo == blas.Upper {
    55  			for i := 0; i < n; i++ {
    56  				if a[i*lda] == 0 {
    57  					return false
    58  				}
    59  			}
    60  		} else {
    61  			for i := 0; i < n; i++ {
    62  				if a[i*lda+kd] == 0 {
    63  					return false
    64  				}
    65  			}
    66  		}
    67  	}
    68  
    69  	// Solve A * X = B  or Aᵀ * X = B.
    70  	bi := blas64.Implementation()
    71  	for j := 0; j < nrhs; j++ {
    72  		bi.Dtbsv(uplo, trans, diag, n, kd, a, lda, b[j:], ldb)
    73  	}
    74  	return true
    75  }