Error in command for partial differentiation

2017 7 14
3 个回答
更新时间：2017 12 29
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0 个投票

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...

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回答（3 个）

Jan
Jan 2017-7-14
编辑：Jan 2017-7-14

0 个投票

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.

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Sergio Manzetti
Sergio Manzetti 2017-7-14
编辑：Sergio Manzetti 2017-7-14
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
Tam Ho 2017-12-29
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!

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Sergio Manzetti
Sergio Manzetti 2017-7-14

0 个投票

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
Sergio Manzetti
Sergio Manzetti 2017-7-14
编辑：Walter Roberson 2017-12-29

0 个投票

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 [.

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Walter Roberson
Walter Roberson 2017-12-29
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()

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