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1 | | -# LLᵀ (Choleski) factorization for symmetric systems |
| 1 | +# LLᵀ (Cholesky) factorization for symmetric systems |
| 2 | + |
| 3 | +function llt_factorization_acyclic!(diagonal_v, offdiagonal_l, diagonal_c, diagonal_inverse_c) |
| 4 | + if diagonal_inverse_c.isinverted |
| 5 | + invdiagonal_c = diagonal_inverse_c.value |
| 6 | + else |
| 7 | + invdiagonal_c = inv(diagonal_c.value) |
| 8 | + diagonal_inverse_c.value = invdiagonal_c |
| 9 | + diagonal_inverse_c.isinverted = true |
| 10 | + end |
| 11 | + offdiagonal_l.value = offdiagonal_l.value * invdiagonal_c |
| 12 | + diagonal_v.value -= offdiagonal_l.value * offdiagonal_l.value' |
| 13 | + return |
| 14 | +end |
| 15 | +function llt_factorization_cyclic!(entry_lu, offdiagonal_lu, offdiagonal_ul) |
| 16 | + entry_lu.value -= offdiagonal_lu.value * offdiagonal_ul.value' |
| 17 | + return |
| 18 | +end |
| 19 | +# TODO currently allocates memory |
| 20 | +function llt_diagonal_root!(diagonal) |
| 21 | + diagonal.value = sqrt(diagonal.value) |
| 22 | +end |
| 23 | + |
| 24 | + |
| 25 | +function llt_factorization!(system::System) |
| 26 | + matrix_entries = system.matrix_entries |
| 27 | + diagonal_inverses = system.diagonal_inverses |
| 28 | + acyclic_children = system.acyclic_children |
| 29 | + cyclic_children = system.cyclic_children |
| 30 | + |
| 31 | + for v in system.dfs_list |
| 32 | + for c in acyclic_children[v] |
| 33 | + llt_factorization_acyclic!(matrix_entries[v,v], matrix_entries[v,c], matrix_entries[c,c], diagonal_inverses[c]) |
| 34 | + end |
| 35 | + for c in cyclic_children[v] |
| 36 | + for cc in cyclic_children[v] |
| 37 | + cc == c && break |
| 38 | + (cc ∉ acyclic_children[c] && cc ∉ cyclic_children[c]) && continue |
| 39 | + llt_factorization_cyclic!(matrix_entries[v,c], matrix_entries[v,cc], matrix_entries[c,cc]) |
| 40 | + end |
| 41 | + llt_factorization_acyclic!(matrix_entries[v,v], matrix_entries[v,c], matrix_entries[c,c], diagonal_inverses[c]) |
| 42 | + end |
| 43 | + llt_diagonal_root!(matrix_entries[v,v]) |
| 44 | + end |
| 45 | + return |
| 46 | +end |
| 47 | + |
| 48 | +function llt_backsubstitution_l!(vector_v, offdiagonal, vector_c) |
| 49 | + vector_v.value -= offdiagonal.value * vector_c.value |
| 50 | + return |
| 51 | +end |
| 52 | +function llt_backsubstitution_lt!(vector_v, offdiagonal, vector_p) |
| 53 | + vector_v.value -= offdiagonal.value' * vector_p.value |
| 54 | + return |
| 55 | +end |
| 56 | +function llt_backsubstitution_d!(vector, diagonal, diagonal_inverse) |
| 57 | + if diagonal_inverse.isinverted |
| 58 | + vector.value = diagonal_inverse.value * vector.value |
| 59 | + else |
| 60 | + invdiagonal = inv(diagonal.value) |
| 61 | + diagonal_inverse.value = invdiagonal |
| 62 | + diagonal_inverse.isinverted = true |
| 63 | + vector.value = diagonal_inverse.value * vector.value |
| 64 | + end |
| 65 | + return |
| 66 | +end |
| 67 | + |
| 68 | +function llt_backsubstitution!(system::System) |
| 69 | + matrix_entries = system.matrix_entries |
| 70 | + diagonal_inverses = system.diagonal_inverses |
| 71 | + vector_entries = system.vector_entries |
| 72 | + acyclic_children = system.acyclic_children |
| 73 | + cyclic_children = system.cyclic_children |
| 74 | + parents = system.parents |
| 75 | + dfs_list = system.dfs_list |
| 76 | + |
| 77 | + for v in dfs_list |
| 78 | + for c in cyclic_children[v] |
| 79 | + llt_backsubstitution_l!(vector_entries[v], matrix_entries[v,c], vector_entries[c]) |
| 80 | + end |
| 81 | + for c in acyclic_children[v] |
| 82 | + llt_backsubstitution_l!(vector_entries[v], matrix_entries[v,c], vector_entries[c]) |
| 83 | + end |
| 84 | + llt_backsubstitution_d!(vector_entries[v], matrix_entries[v,v], diagonal_inverses[v]) |
| 85 | + end |
| 86 | + for v in reverse(dfs_list) |
| 87 | + for p in parents[v] |
| 88 | + llt_backsubstitution_lt!(vector_entries[v], matrix_entries[p,v], vector_entries[p]) |
| 89 | + end |
| 90 | + llt_backsubstitution_d!(vector_entries[v], matrix_entries[v,v], diagonal_inverses[v]) |
| 91 | + end |
| 92 | +end |
| 93 | + |
| 94 | +function llt_solve!(system::System) |
| 95 | + reset_inverse_diagonals!(system) |
| 96 | + llt_factorization!(system) |
| 97 | + llt_backsubstitution!(system) |
| 98 | + return |
| 99 | +end |
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