|
| 1 | +module Internal |
| 2 | + |
| 3 | +import ForwardDiff # TODO: remove the dependency on ForwardDiff.jl |
| 4 | +import LogDensityProblems |
| 5 | +import LinearAlgebra |
| 6 | +import TransformVariables |
| 7 | + |
| 8 | +const _default_fuzz_factor = 0.01 |
| 9 | + |
| 10 | +function gradient_vector(transformed_gradient_problem, |
| 11 | + theta) |
| 12 | + transformed_log_density = parent(transformed_gradient_problem) |
| 13 | + transformation = transformed_log_density.transformation |
| 14 | + theta_inversetransformed = TransformVariables.inverse(transformation, |
| 15 | + theta) |
| 16 | + result = _gradient_vector(transformed_gradient_problem, |
| 17 | + theta_inversetransformed) |
| 18 | + return result |
| 19 | +end |
| 20 | + |
| 21 | +function _gradient_vector(transformed_gradient_problem, |
| 22 | + theta) |
| 23 | + log_likelihood_value, gradient = LogDensityProblems.logdensity_and_gradient(transformed_gradient_problem, |
| 24 | + theta) |
| 25 | + return gradient |
| 26 | +end |
| 27 | + |
| 28 | +function hessian_matrix(transformed_gradient_problem, |
| 29 | + theta) |
| 30 | + transformed_log_density = parent(transformed_gradient_problem) |
| 31 | + transformation = transformed_log_density.transformation |
| 32 | + theta_inversetransformed = TransformVariables.inverse(transformation, |
| 33 | + theta) |
| 34 | + result = _hessian_matrix(transformed_gradient_problem, |
| 35 | + theta_inversetransformed) |
| 36 | + return result |
| 37 | +end |
| 38 | + |
| 39 | +function _hessian_matrix(transformed_gradient_problem, |
| 40 | + theta) |
| 41 | + @assert transformed_gradient_problem isa LogDensityProblems.ForwardDiffLogDensity |
| 42 | + ℓ = transformed_gradient_problem.ℓ |
| 43 | + logdensity_closure = LogDensityProblems._logdensity_closure(ℓ) |
| 44 | + hessian = ForwardDiff.hessian(logdensity_closure, |
| 45 | + theta) |
| 46 | + return hessian |
| 47 | +end |
| 48 | + |
| 49 | +function _is_approximately_zero(a::AbstractArray; |
| 50 | + tolerance = 1e-4) |
| 51 | + result = all( abs.(a) .< tolerance ) |
| 52 | + return result |
| 53 | +end |
| 54 | + |
| 55 | +function _is_approximately_hermitian(m::AbstractMatrix; |
| 56 | + tolerance = 1e-4) |
| 57 | + LinearAlgebra.checksquare(m) |
| 58 | + result = _is_approximately_zero(m - LinearAlgebra.adjoint(m); |
| 59 | + tolerance = tolerance) |
| 60 | + return result |
| 61 | +end |
| 62 | + |
| 63 | +function _all_eigenvalues_are_negative(m::AbstractMatrix; |
| 64 | + fuzz_factor = _default_fuzz_factor) |
| 65 | + eigvals = LinearAlgebra.eigvals(m) |
| 66 | + a = all( eigvals .< 0 ) |
| 67 | + b = all( eigvals .< -abs(fuzz_factor) ) |
| 68 | + result = a && b |
| 69 | + return result |
| 70 | +end |
| 71 | + |
| 72 | +function _all_eigenvalues_are_positive(m::AbstractMatrix; |
| 73 | + fuzz_factor = _default_fuzz_factor) |
| 74 | + eigvals = LinearAlgebra.eigvals(m) |
| 75 | + a = all( eigvals .> 0 ) |
| 76 | + b = all( eigvals .> abs(fuzz_factor) ) |
| 77 | + result = a && b |
| 78 | + return result |
| 79 | +end |
| 80 | + |
| 81 | +function _is_approximately_negative_definite(m::AbstractMatrix; |
| 82 | + tolerance = 1e-4, |
| 83 | + fuzz_factor = _default_fuzz_factor) |
| 84 | + # Let `m` be a Hermitian matrix. Then `m` is negative |
| 85 | + # definite if and only if all of its eigenvalues are |
| 86 | + # negative. |
| 87 | + a = _is_approximately_hermitian(m; |
| 88 | + tolerance = tolerance) |
| 89 | + b = _all_eigenvalues_are_negative(m; |
| 90 | + fuzz_factor = fuzz_factor) |
| 91 | + result = a && b |
| 92 | + return result |
| 93 | +end |
| 94 | + |
| 95 | +function _is_approximately_positive_definite(m::AbstractMatrix; |
| 96 | + tolerance = 1e-4, |
| 97 | + fuzz_factor = _default_fuzz_factor) |
| 98 | + # Let `m` be a Hermitian matrix. Then `m` is positive |
| 99 | + # definite if and only if all of its eigenvalues are |
| 100 | + # positive. |
| 101 | + a = _is_approximately_hermitian(m; |
| 102 | + tolerance = tolerance) |
| 103 | + b = _all_eigenvalues_are_positive(m; |
| 104 | + fuzz_factor = fuzz_factor) |
| 105 | + result = a && b |
| 106 | + return result |
| 107 | +end |
| 108 | + |
| 109 | +end # module |
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