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Give a warning for underconstrained variables forced to 0 #2328

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e34f3de
Give a warning for underconstrained variables forced to 0
Keno Oct 25, 2023
5dc99b7
Merge branch 'master' into kf/unconstrainedwarning
YingboMa Oct 28, 2023
6dd475e
Merge branch 'master' into kf/unconstrainedwarning
YingboMa Mar 26, 2024
09f2122
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YingboMa Mar 26, 2024
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44 changes: 30 additions & 14 deletions src/systems/alias_elimination.jl
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Original file line number Diff line number Diff line change
@@ -1,14 +1,15 @@
using SymbolicUtils: Rewriters
using Graphs.Experimental.Traversals

function alias_eliminate_graph!(state::TransformationState; kwargs...)
function alias_eliminate_graph!(state::TransformationState;
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@YingboMa YingboMa Oct 25, 2023 •
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We need to make warning reporting an option here, because sometimes MTK performs transformations that leave harmless dangling variables.

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The default here is not to warn. The warning is in the higher level function in alias_elimination! that has access to the variables. If you can tell which variables are harmless, you can suppress the warning there.

variable_underconstrained! = force_var_to_zero!, kwargs...)
mm = linear_subsys_adjmat!(state; kwargs...)
if size(mm, 1) == 0
return mm # No linear subsystems
end

@unpack graph, var_to_diff, solvable_graph = state.structure
mm = alias_eliminate_graph!(state, mm)
mm = alias_eliminate_graph!(state, mm; variable_underconstrained!)
s = state.structure
for g in (s.graph, s.solvable_graph)
g === nothing && continue
Expand Down Expand Up @@ -47,9 +48,17 @@ function alias_elimination!(state::TearingState; kwargs...)
sys = state.sys
complete!(state.structure)
graph_orig = copy(state.structure.graph)
mm = alias_eliminate_graph!(state; kwargs...)

fullvars = state.fullvars

function variable_underconstrained_mtk!(structure::SystemStructure,
ils::SparseMatrixCLIL,
v::Int)
@warn "The model is under-constrained. Variable $(fullvars[v]) was arbitrarily chosen to be set to 0. This may indicate a model bug!"
return force_var_to_zero!(structure, ils, v)
end
mm = alias_eliminate_graph!(state;
variable_underconstrained! = variable_underconstrained_mtk!, kwargs...)

@unpack var_to_diff, graph, solvable_graph = state.structure

subs = Dict()
Expand Down Expand Up @@ -347,7 +356,22 @@ function do_bareiss!(M, Mold, is_linear_variables, is_highest_diff)
(rank1, rank2, rank3, pivots)
end

function alias_eliminate_graph!(state::TransformationState, ils::SparseMatrixCLIL)
function force_var_to_zero!(structure::SystemStructure, ils::SparseMatrixCLIL, v::Int)
@unpack graph, solvable_graph, eq_to_diff = structure
@set! ils.nparentrows += 1
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This call needs to return ils because @set! creates a new object.

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Good catch, I thought it was mutable, but of course it isn't.

push!(ils.nzrows, ils.nparentrows)
push!(ils.row_cols, [v])
push!(ils.row_vals, [convert(eltype(ils), 1)])
add_vertex!(graph, SRC)
add_vertex!(solvable_graph, SRC)
add_edge!(graph, ils.nparentrows, v)
add_edge!(solvable_graph, ils.nparentrows, v)
add_vertex!(eq_to_diff)
return ils
end

function alias_eliminate_graph!(state::TransformationState, ils::SparseMatrixCLIL;
variable_underconstrained! = force_var_to_zero!)
@unpack structure = state
@unpack graph, solvable_graph, var_to_diff, eq_to_diff = state.structure
# Step 1: Perform Bareiss factorization on the adjacency matrix of the linear
Expand All @@ -359,15 +383,7 @@ function alias_eliminate_graph!(state::TransformationState, ils::SparseMatrixCLI
rk1vars = BitSet(@view pivots[1:rank1])
for v in solvable_variables
v in rk1vars && continue
@set! ils.nparentrows += 1
push!(ils.nzrows, ils.nparentrows)
push!(ils.row_cols, [v])
push!(ils.row_vals, [convert(eltype(ils), 1)])
add_vertex!(graph, SRC)
add_vertex!(solvable_graph, SRC)
add_edge!(graph, ils.nparentrows, v)
add_edge!(solvable_graph, ils.nparentrows, v)
add_vertex!(eq_to_diff)
ils = variable_underconstrained!(structure, ils, v)
end

return ils
Expand Down