The error in this MATLAB code is due to the incorrect use of the variable x in the integral calculation.
In the line that calculates the integral, the expression ((x.^4).*exp(x))./((exp(x)-1)^2) is used as the integrand. However, x has not been defined before, so MATLAB does not know what value to use for it. This causes an error, because the integral function needs a valid function handle to compute the integral.
To fix the error, you can modify the code to define x as the integration variable and use it in the integrand expression. Here's the corrected code:
k = 1.38e-23;
N = 6e23;
Td = 323;
T = 0:2*Td;
for i = 1:length(T)
I = integral(@(x) ((x.^4).*exp(x))./((exp(x)-1).^2), 0, T(i)/Td);
Cvd(i) = 9*N*k*I*(T(i)/Td)^3;
end
plot(T, Cvd)
In this corrected code, x is defined as the integration variable in the anonymous function @(x), and is used in the expression for the integrand. Also, note that T(i)/Td is used to define the upper limit of the integral, because the upper limit depends on the current value of T(i) being iterated over.
