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Add cancellation of common variables in 'simplify' #24

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556d2e5
Add cancellation of common variables in 'simplify'
magistere Oct 24, 2013
54539c7
Code clarification
magistere Oct 25, 2013
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25 changes: 25 additions & 0 deletions src/symbolic.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -129,6 +129,29 @@ function mul_numeric_args(args)
(prod, sym_args)
end

cancel_common(num, den) = (num, den)
cancel_common(num::Symbol, den::Symbol) = num==den ? (1, 1) : (num, den)
cancel_common(num::Expr, den::Symbol) = cancel_common(num, Expr(:call, :*, den))
cancel_common(num::Symbol, den::Expr) = cancel_common(Expr(:call, :*, num), den)

function cancel_common(num::Expr, den::Expr)
if num.args[1] != :* || den.args[1] != :*
return (num, den)
end
an = num.args[2:end]
ad = den.args[2:end]
i = 1
while i <= length(ad)
idx = findfirst(an, ad[i])
if idx != 0
splice!(ad, i)
splice!(an, idx)
end
i += 1
end
(Expr(:call, :*, an...), Expr(:call, :*, ad...))
end

# Handle `args` of all lengths
function simplify(::SymbolParameter{:+}, args)
# Remove any 0's in a sum
Expand Down Expand Up @@ -188,6 +211,8 @@ function simplify(::SymbolParameter{:/}, args)
elseif args[1] == 0
return 0
else
args = cancel_common(args[1], args[2])
args = map(simplify, args)
return Expr(:call, :/, args...)
end
end
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8 changes: 8 additions & 0 deletions test/symbolic.jl
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Expand Up @@ -88,3 +88,11 @@ end
@test isequal(simplify(:(x*3)), :(*(3,x)))
@test isequal(simplify(:(x*3*4)), :(*(12,x)))
@test isequal(simplify(:(2*y*x*3)), :(*(6,y,x)))

@test isequal(simplify(:(x/x)), 1.0)
@test isequal(simplify(:((2*x)/x)), 2.0)
@test isequal(simplify(:(x/(2*x))), 0.5)
@test isequal(simplify(:((2*y)/x)), :(/(*(2,y),x)))
@test isequal(simplify(:((5*x)/(2*x))), 2.5)
@test isequal(simplify(:((y*x*5)/(2*x))), :(5*y/2))
@test isequal(simplify(:((5*z)/(2*x))), :((5*z)/(2*x)))