How to separate negative and positive terms in to two different expressions

I am using symolic vavriables

syms a b c d f g

Where all syms variables are positive

and have, for example the following expression A

F=a- b*d+ g*c-a*c+ d*g

my actual expression is much longer but how can I separate the negative vs the positive terms and put them in say in x and y?

I appreciate any help .

Thank you!

Answer 1

[Ameer Hamza]

Try this

syms a b c d f g

F = a - b*d + g*c - a*c + d*g;
parts = children(F);
parts = [parts{:}];
assume(symvar(parts)>0)
sgns = sign(parts);
assume(symvar(parts), 'clear')

x = parts(sgns==1);
y = parts(sgns==-1);

[EllaD]

Thanks Ameer it gives me error saying :

Error using sym/subsref

Too many output arguments.

Error in (line 6)

parts = [parts{:}];

[Ameer Hamza]

Which MATLAB release are you using? You may be able create a cell array

syms a b c d f g

F = a - b*d + g*c - a*c + d*g;
parts = children(F);
assume([a b c d f g]>0)
sgns = cellfun(@sign, parts);
assume([a b c d f g], 'clear')

x = parts(sgns==1);
y = parts(sgns==-1);

[EllaD]

gives this:

Error using cellfun

Input #2 expected to be a cell array, was sym instead.

Error in negativepositive (line 17)

sgns = cellfun(@sign, parts);

it is 2012a . But thanks anyways Ameer :) I will be going for an upgrade, it is way old I guess.

[Ameer Hamza]

Yes, it seems something related to old release. It seems that children() does not return a cell array in your case.