Conversion to double from sym is not possible

Question

Tyler 2011-11-14

回答： Shahid Iqbal 2019-6-30

syms n;
t = (-300:1:300);
D_n = ((sin((pi*n)/2))./(pi*n));
y = (D_n).*exp((-j)*n*t*(pi/100));
x = symsum(y,n,-10,-1) + symsum(y,n,1,10);
plot(t,x);

I would like to plot t vs. x, however I get the error 'Conversion to double from sym is not possible'.

Christopher Creutzig 2011-11-17

Works fine for me. Are you using exactly the commands listed above? Which MATLAB version are you using? What does symvar(x) tell you?

Answer 1

Walter Roberson 2011-11-14

Your x is a formula in terms of n, a variable you do not define a value for at any point.

Your t value has nothing to do with n.

You cannot plot a symbolic expression against an unrelated variable.

Perhaps what you want is

plot(t, double(subs(x,n,t)))

BecauseHElives 2014-2-4

I had the same problem. This answer works.

Answer 2

Shahid Iqbal 2019-6-30

syms n;
t = (-300:1:300);
D_n = ((sin((pi*n)/2))./(pi*n));
y = (D_n).*exp((-1i)*n*t*(pi/100));
x = symsum(y,n,-10,-1) + symsum(y,n,1,10);
plot(t,x);

work properly just replace -j with -1i , use updated version of MATLAB.