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// Copyright ©2019 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 "gonum.org/v1/gonum/blas"
// Dpotri computes the inverse of a real symmetric positive definite matrix A
// using its Cholesky factorization.
//
// On entry, a contains the triangular factor U or L from the Cholesky
// factorization A = Uᵀ*U or A = L*Lᵀ, as computed by Dpotrf.
// On return, a contains the upper or lower triangle of the (symmetric)
// inverse of A, overwriting the input factor U or L.
func (impl Implementation) Dpotri(uplo blas.Uplo, n int, a []float64, lda int) (ok bool) {
switch {
case uplo != blas.Upper && uplo != blas.Lower:
panic(badUplo)
case n < 0:
panic(nLT0)
case lda < max(1, n):
panic(badLdA)
}
// Quick return if possible.
if n == 0 {
return true
}
if len(a) < (n-1)*lda+n {
panic(shortA)
}
// Invert the triangular Cholesky factor U or L.
ok = impl.Dtrtri(uplo, blas.NonUnit, n, a, lda)
if !ok {
return false
}
// Form inv(U)*inv(U)ᵀ or inv(L)ᵀ*inv(L).
impl.Dlauum(uplo, n, a, lda)
return true
}
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