Having trouble finding a derivative

Im fairly new to matlab and I keep getting the same error message.

When the following is entered: diff cot^2(sin theta)

I get:

Error using sym>convertExpression (line 2256) Conversion to 'sym' returned the MuPAD error: Error: Unexpected 'identifier'. [line 1, col 11]

Error in sym>convertChar (line 2167) s = convertExpression(x);

Error in sym>convertCharWithOption (line 2150) s = convertChar(x);

Error in sym>tomupad (line 1881) S = convertCharWithOption(x,a);

Error in sym (line 108) S.s = tomupad(x,'');

Error in char/diff (line 11) y = diff(sym(f),varargin{:});

Would appreciate any help or guidance thank you.

Answer 1

[Walter Roberson]

syms theta
diff( cot(sin(theta))^2, theta)

[Frank]

Awesome thank you!

[Tam Ho]

I ran this code:

   syms theta %create symbolic variable theta
assume(theta,'real') %theta is real
f = fit_v2; %calling our fitted polynomials

g = diff(f,theta);
g0=solve(g,theta);
double(g0);

I get this error:

Error in sym (line 215)
              S.s = tomupad(x);

Error in sym/privResolveArgs (line 988)
                  argout{k} = sym(arg);

Error in sym/diff (line 21)
args = privResolveArgs(S,varargin{:});

Error in code (line 54)
g = diff(f,theta);

[Walter Roberson]

What is fit_v2 ?