| // Copyright ©2015 The gonum Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| package gonum |
| |
| import ( |
| "math" |
| |
| "gonum.org/v1/gonum/blas" |
| "gonum.org/v1/gonum/blas/blas64" |
| ) |
| |
| // Dpotf2 computes the Cholesky decomposition of the symmetric positive definite |
| // matrix a. If ul == blas.Upper, then a is stored as an upper-triangular matrix, |
| // and a = U^T U is stored in place into a. If ul == blas.Lower, then a = L L^T |
| // is computed and stored in-place into a. If a is not positive definite, false |
| // is returned. This is the unblocked version of the algorithm. |
| // |
| // Dpotf2 is an internal routine. It is exported for testing purposes. |
| func (Implementation) Dpotf2(ul blas.Uplo, n int, a []float64, lda int) (ok bool) { |
| if ul != blas.Upper && ul != blas.Lower { |
| panic(badUplo) |
| } |
| checkMatrix(n, n, a, lda) |
| |
| if n == 0 { |
| return true |
| } |
| |
| bi := blas64.Implementation() |
| if ul == blas.Upper { |
| for j := 0; j < n; j++ { |
| ajj := a[j*lda+j] |
| if j != 0 { |
| ajj -= bi.Ddot(j, a[j:], lda, a[j:], lda) |
| } |
| if ajj <= 0 || math.IsNaN(ajj) { |
| a[j*lda+j] = ajj |
| return false |
| } |
| ajj = math.Sqrt(ajj) |
| a[j*lda+j] = ajj |
| if j < n-1 { |
| bi.Dgemv(blas.Trans, j, n-j-1, |
| -1, a[j+1:], lda, a[j:], lda, |
| 1, a[j*lda+j+1:], 1) |
| bi.Dscal(n-j-1, 1/ajj, a[j*lda+j+1:], 1) |
| } |
| } |
| return true |
| } |
| for j := 0; j < n; j++ { |
| ajj := a[j*lda+j] |
| if j != 0 { |
| ajj -= bi.Ddot(j, a[j*lda:], 1, a[j*lda:], 1) |
| } |
| if ajj <= 0 || math.IsNaN(ajj) { |
| a[j*lda+j] = ajj |
| return false |
| } |
| ajj = math.Sqrt(ajj) |
| a[j*lda+j] = ajj |
| if j < n-1 { |
| bi.Dgemv(blas.NoTrans, n-j-1, j, |
| -1, a[(j+1)*lda:], lda, a[j*lda:], 1, |
| 1, a[(j+1)*lda+j:], lda) |
| bi.Dscal(n-j-1, 1/ajj, a[(j+1)*lda+j:], lda) |
| } |
| } |
| return true |
| } |