Merge pull request #1398 from AayushSabharwal/as/fast-substitute-array

fix: fix `fast_substitute` folding array of symbolics

Author: ChrisRackauckas

Project.toml

@@ -92,7 +92,7 @@ StaticArraysCore = "1.4"
 SymPy = "2.2"
 SymbolicIndexingInterface = "0.3.14"
 SymbolicLimits = "0.2.2"
-SymbolicUtils = "3.7"
+SymbolicUtils = "3.10"
 TermInterface = "2"
 julia = "1.10"
 

src/solver/preprocess.jl

@@ -135,7 +135,7 @@ function _filter_poly(expr, var)
         subs[i_var] = im
         expr = unwrap(expr1 + i_var * expr2)
 
-        args = arguments(expr)
+        args = map(unwrap, arguments(expr))
         oper = operation(expr)
         return subs, term(oper, args...)
     end
@@ -208,7 +208,7 @@ function _filter_poly(expr, var)
         end
     end
 
-    args = arguments(expr)
+    args = map(unwrap, arguments(expr))
     oper = operation(expr)
     expr = term(oper, args...)
     return subs, expr

src/variable.jl

@@ -606,7 +606,7 @@ function fast_substitute(expr, subs; operator = Nothing)
         args = let canfold = canfold
             map(args) do x
                 x′ = fast_substitute(x, subs; operator)
-                canfold[] = canfold[] && !(x′ isa Symbolic)
+                canfold[] = canfold[] && (symbolic_type(x′) == NotSymbolic() && !is_array_of_symbolics(x′))
                 x′
             end
         end
@@ -633,7 +633,7 @@ function fast_substitute(expr, pair::Pair; operator = Nothing)
         args = let canfold = canfold
             map(args) do x
                 x′ = fast_substitute(x, pair; operator)
-                canfold[] = canfold[] && !(x′ isa Symbolic)
+                canfold[] = canfold[] && (symbolic_type(x′) == NotSymbolic() && !is_array_of_symbolics(x′))
                 x′
             end
         end
@@ -645,6 +645,13 @@ function fast_substitute(expr, pair::Pair; operator = Nothing)
         metadata(expr))
 end
 
+function is_array_of_symbolics(x)
+    symbolic_type(x) == ArraySymbolic() && return true
+    symbolic_type(x) == ScalarSymbolic() && return false
+    x isa AbstractArray &&
+        any(y -> symbolic_type(y) != NotSymbolic() || is_array_of_symbolics(y), x)
+end
+
 function getparent(x, val=_fail)
     maybe_parent = getmetadata(x, Symbolics.GetindexParent, nothing)
     if maybe_parent !== nothing

test/arrays.jl

@@ -388,7 +388,7 @@ end
     lapu = wrap(lapu)
     lapv = wrap(lapv)
 
-    f, g = build_function(dtu, u, v, t, expression=Val{false})
+    f, g = build_function(dtu, u, v, t, expression=Val{false}, nanmath = false)
     du = zeros(Num, 8, 8)
     f(du, u,v,t)
     @test isequal(collect(du), collect(dtu))

test/utils.jl

@@ -153,4 +153,12 @@ end
     test_nested_derivative = Dx(Dt(Dt(u)))
     result = diff2term(Symbolics.value(test_nested_derivative))
     @test typeof(result) === Symbolics.BasicSymbolic{Real}
-end
+end
+
+@testset "`fast_substitute` inside array symbolics" begin
+    @variables x y z
+    @register_symbolic foo(a::AbstractArray, b)
+    ex = foo([x, y], z)
+    ex2 = Symbolics.fixpoint_sub(ex, Dict(y => 1.0, z => 2.0))
+    @test isequal(ex2, foo([x, 1.0], 2.0))
+end