why I'm getting error with symsum?

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geometry geometry 2018-3-19

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https://ww2.mathworks.cn/matlabcentral/answers/389156-why-i-m-getting-error-with-symsum

评论： Walter Roberson 2018-3-19

I have tried this code to calculate energy and power of discrete time functions. but I get errors. how can I fix it?

syms n f z N;
f=input('enter function: ','s');
f = symfun(eval(f), n);
f=f*conj(f);
f = matlabFunction(f);
y(N)=symsum(f, -N , N);
energy=limit(y(N),N,inf);
z(N)=y(N)/(2*N+1);
pow=limit(z(N),N,inf);

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geometry geometry 2018-3-19

编辑：geometry geometry 2018-3-19

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I changed the code and tried without symsum and using "for" but again I get a lot of errors:

syms f n y x Z p s H i E P
E=0;
P=0;
H(n)=heaviside(n)+(1/2)*piecewise(n==0,1,0);
%x(n)=piecewise(n==0,1,0)+piecewise(n==4,1,0)-2*heaviside(n+3)+2*heaviside(n-3);
%Z(n)=(-1)^(n)*cos(n*pi/2)*x(n);
f=input('enter function: ');
f=f*conj(f);
f = matlabFunction(f);
for i=-N:N
  E=E+f(i);
end
P(N)=E/(2*N+1);
E=limit(E(N),N,inf);
P=limit(P(N),N,inf);