MATLAB: Error using plot. Trying to plot function

functionmatrixplot

I am trying to plot a function Q11 of x. I get an error "Error using plot. A numeric or double convertible argument is expected." My Q11 is a function of x which I set a range for. Any help would be appreciated.
clc
clear all
syms x
%%KNOWN VARIABLES
E1 = 19; %MPA


E2 = 1.5; %MPA
G12 = 1.0; %MPA
v12 = .22;
v21 = v12*(E2/E1);
%%Q & S MATRIX
S = [1/E1 -v21/E2 0;...
   -v12/E1 1/E2 0;...
   0 0 1/G12];
Q = inv(S);
%%T, R, & Q* MATRIX
T = [(cos(x))^2, (sin(x))^2, -2*cos(x)*sin(x);...
   (sin(x))^2, (cos(x))^2, 2*cos(x)*sin(x);...
   cos(x)*sin(x), -1*cos(x)*sin(x), (cos(x)^2)-(sin(x)^2)];
R = [1 0 0; 0 1 0; 0 0 2]; 
Q_star = Q*R;
%%SOLUTION FOR Q_bar
Q_bar = inv(T) * Q_star * T * inv(R);
Q11 = Q_bar(1,1)
x = -1.5708:.087:1.5708;
plot(x,Q11)

Best Answer

plot(x, subs(Q11, 'x', x))
or more briefly,
plot(x, subs(Q11))
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