error when using diff() on trigonometric functions

Hello,

When i try to apply this in matlab:

syms x
diff(cos(x))

I get :

ans =
diff(cos(x), x)

Instead of -sin(x) as expected. The examples and help show that it should work for trig functions and I don't understand why this isn't working for me.

Is this a kind of bug? Has anyone encountered this before?

Thanks, Alex

[Wayne King]

Can you please give which version of MATLAB you are using? Thanks

[alex pabouctsidis]

I'm using R2012b

[Jan]

Did you create a variable or function called "cos" before?

[alex pabouctsidis]

I had a syms cos(phi) for another variable, which in hindsight was a bit dumb :P

i removed it and it works now.

thanks!