Error in command for partial differentiation

Hi, I am trying to run this simple command:

y*(x*(exp(-i*(x+y)) - diff((exp(-i*(x+y)), x)) - x*diff((exp(-i*(x+y)), y) + diff((exp(-i*(x+y)), x, y)

however MATLAB doesn't take it and says:

Error: Expression or statement is incorrect--possibly unbalanced (, {, or [.

However, the brackets are balanced...

Answer 1

[Jan]

Seriously? Matlab tells you clearly, that the parenthesis are not balanced and you do not believe it?

c = ['y*(x*(exp(-i*(x+y)) - diff((exp(-i*(x+y)), x)) - ', ...
     'x*diff((exp(-i*(x+y)), y) + diff((exp(-i*(x+y)), x, y)']
sum(c == '(')   % >> 16
sum(c == ')')   % >> 12

There are 4 unclosed parenthesis. Ups. I recommend to trust Matlab's error messages.

[Sergio Manzetti]

Yet again:

f(x,y) = exp(-i.*x)

      if true
        % code
      end
y*x*f(x,y) - diff(f(x,y), x) - x*diff(f(x,y), y) + diff(f(x,y), x, y);

Nothing happens

[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);

please help! Thanks!

[Walter Roberson]

What is fit_v2 ?

Answer 2

[Sergio Manzetti]

John ,please see closer, I have removed one redundant bracket after the y at the beginning, otherwise, it is fine:

y*x*(exp(-i*(x+y)) - diff((exp(-i*(x+y)), x)) - x*diff((exp(-i*(x+y)), y) + diff((exp(-i*(x+y)), x, y))

Nothing is missing here or superfluous

Answer 3

[Sergio Manzetti]

Have a look at this short example:

>> diff((exp(-i*(x+y)), x))
 diff((exp(-i*(x+y)), x))
                    ↑
Error: Expression or statement is incorrect--possibly unbalanced (, {, or [.

[Walter Roberson]

diff(exp(-i*(x+y)), x)

or

diff((exp(-i*(x+y))), x)

If you examine

diff((exp(-i*(x+y)), x))

you will see that the first argument is

(exp(-i*(x+y)), x)

which is an invalid sequence, since MATLAB does not permit expression comma expression inside anything other than [] or {} . You are also not passing a second argument to diff()