Finding similar symbolic expressions in a vector

Hey guys, i have following problem:

Let there be a long vector containing symbolic expressions. To reduce the vector length i try to find elements which are correlated (i don't know if that is the right word for what i mean, maybe an example will help).

For example:

v = [a, b^2+c, d^4/e, -a+b^2+c, -a].'

Here is v(5)=-v(1) or the other way round. And v(4)=-v(1)+v(2)

There might exist other combinations, but these i can see directly.

The big question is: Is there a function or some functions i can use, or should i iterate the whole vector and compare each row to the others?

The first problem (v(x) = t*v(y) where t is a constant, x and y are some rows in the vector) is easier than the second one i think.

I tried some combinations of unique and sort, but unique only shows me identical lines, not similar ones.

Any ideas? Thank you very much :)

ps : i use matlab 2011a

Answer 1

[Star Strider]

To start, I suggest children:

syms a b c d e 
v = [a, b^2+c, d^4/e, -a+b^2+c, -a].'
cv = children(v)
cv{1:5}

I have 2012b but I believe this is also available in 2011a.

[Jan Kappen]

Nice idea, but unfortunately children does not exist in 2011a.

[Star Strider]

Sorry.

In that situation, I suggest subexpr, the only other alternative I can find. It should exist in 2011a.

You can use subexpr iteratively:

syms a b c d e 
v = [a, b^2+c, d^4/e, -a+b^2+c, -a].'
[r1,s1] = subexpr(v, 'S1')
[r2,s2] = subexpr(r1, 'S2')