github.com/gonum/lapack@v0.0.0-20181123203213-e4cdc5a0bff9/native/dorml2.go (about)

     1  // Copyright ©2015 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 native
     6  
     7  import "github.com/gonum/blas"
     8  
     9  // Dorml2 multiplies a general matrix C by an orthogonal matrix from an LQ factorization
    10  // determined by Dgelqf.
    11  //  C = Q * C    if side == blas.Left and trans == blas.NoTrans
    12  //  C = Q^T * C  if side == blas.Left and trans == blas.Trans
    13  //  C = C * Q    if side == blas.Right and trans == blas.NoTrans
    14  //  C = C * Q^T  if side == blas.Right and trans == blas.Trans
    15  // If side == blas.Left, a is a matrix of side k×m, and if side == blas.Right
    16  // a is of size k×n.
    17  //
    18  // tau contains the Householder factors and is of length at least k and this function will
    19  // panic otherwise.
    20  //
    21  // work is temporary storage of length at least n if side == blas.Left
    22  // and at least m if side == blas.Right and this function will panic otherwise.
    23  //
    24  // Dorml2 is an internal routine. It is exported for testing purposes.
    25  func (impl Implementation) Dorml2(side blas.Side, trans blas.Transpose, m, n, k int, a []float64, lda int, tau, c []float64, ldc int, work []float64) {
    26  	if side != blas.Left && side != blas.Right {
    27  		panic(badSide)
    28  	}
    29  	if trans != blas.Trans && trans != blas.NoTrans {
    30  		panic(badTrans)
    31  	}
    32  
    33  	left := side == blas.Left
    34  	notran := trans == blas.NoTrans
    35  	if left {
    36  		checkMatrix(k, m, a, lda)
    37  		if len(work) < n {
    38  			panic(badWork)
    39  		}
    40  	} else {
    41  		checkMatrix(k, n, a, lda)
    42  		if len(work) < m {
    43  			panic(badWork)
    44  		}
    45  	}
    46  	checkMatrix(m, n, c, ldc)
    47  	if m == 0 || n == 0 || k == 0 {
    48  		return
    49  	}
    50  	switch {
    51  	case left && notran:
    52  		for i := 0; i < k; i++ {
    53  			aii := a[i*lda+i]
    54  			a[i*lda+i] = 1
    55  			impl.Dlarf(side, m-i, n, a[i*lda+i:], 1, tau[i], c[i*ldc:], ldc, work)
    56  			a[i*lda+i] = aii
    57  		}
    58  
    59  	case left && !notran:
    60  		for i := k - 1; i >= 0; i-- {
    61  			aii := a[i*lda+i]
    62  			a[i*lda+i] = 1
    63  			impl.Dlarf(side, m-i, n, a[i*lda+i:], 1, tau[i], c[i*ldc:], ldc, work)
    64  			a[i*lda+i] = aii
    65  		}
    66  
    67  	case !left && notran:
    68  		for i := k - 1; i >= 0; i-- {
    69  			aii := a[i*lda+i]
    70  			a[i*lda+i] = 1
    71  			impl.Dlarf(side, m, n-i, a[i*lda+i:], 1, tau[i], c[i:], ldc, work)
    72  			a[i*lda+i] = aii
    73  		}
    74  
    75  	case !left && !notran:
    76  		for i := 0; i < k; i++ {
    77  			aii := a[i*lda+i]
    78  			a[i*lda+i] = 1
    79  			impl.Dlarf(side, m, n-i, a[i*lda+i:], 1, tau[i], c[i:], ldc, work)
    80  			a[i*lda+i] = aii
    81  		}
    82  	}
    83  }