Merge pull request #384 from JuliaSymbolics/s/as_polynomial

as_polynomial

Author: shashi

src/polyform.jl

@@ -1,4 +1,4 @@
-export PolyForm, simplify_fractions, quick_cancel, flatten_fractions
+export PolyForm, simplify_fractions, quick_cancel, flatten_fractions, as_polynomial
 using Bijections
 using DynamicPolynomials: PolyVar
 
@@ -43,6 +43,34 @@ end
 Base.hash(p::PolyForm, u::UInt64) = xor(hash(p.p, u),  trunc(UInt, 0xbabacacababacaca))
 Base.isequal(x::PolyForm, y::PolyForm) = isequal(x.p, y.p)
 
+
+function as_polynomial(f, exprs...; polyform=false, T=Real)
+    @assert length(exprs) >= 1 "At least one expression must be passed to `multivariatepolynomial`."
+
+    pvar2sym, sym2term = get_pvar2sym(), get_sym2term()
+    ps = map(exprs) do x
+        if istree(x) && operation(x) == (/)
+            num, den = arguments(x)
+            PolyForm(num, pvar2sym, sym2term).p /
+            PolyForm(den, pvar2sym, sym2term).p
+        else
+            PolyForm(x, pvar2sym, sym2term).p
+        end
+    end
+
+    convert_back_f = function (x)
+        if x isa MultivariatePolynomials.RationalPoly
+            PolyForm{T}(numerator(x), pvar2sym, sym2term) /
+            PolyForm{T}(denominator(x), pvar2sym, sym2term)
+        else
+            PolyForm{T}(x, pvar2sym, sym2term)
+        end
+    end
+
+    convert_back = polyform ? convert_back_f : unpolyize ∘ convert_back_f
+    res = f(convert_back, ps...)
+end
+
 # We use the same PVAR2SYM bijection to maintain the PolyVar <-> Sym mapping,
 # When all PolyForms go out of scope in a session, we allow it to free up memory and
 # start over if necessary

test/polyform.jl

@@ -76,3 +76,17 @@ end
     @test !SymbolicUtils.fraction_isone(x)
     @test SymbolicUtils.fraction_isone(o)
 end
+
+
+@testset "as_polynomial" begin
+
+    @syms x y z
+    @eqtest as_polynomial((f, x, y) -> f(gcd(x, y)), 10x+10y, 5*(x^2-y^2)) == 5x + 5y
+    @test as_polynomial((f, x, y) -> f(gcd(x, y)), 10x+10y, 5*(x^2-y^2), polyform=true) isa PolyForm
+    @test repr(as_polynomial((f, x, y) -> f(gcd(x, y)), 10x+10y, 5*(x^2-y^2), polyform=true)) == repr(5x + 5y)
+
+
+    @test as_polynomial(x, y/z) do g, x, y
+        g(x+y)
+    end |> repr == "(y + x*z) / z"
+end