Error while trying to use diff comand

This is the code that I created and I am trying to differentiate Id and Vt but every time I run the program I keep getting this error, "Difference order N must be a positive integer scalar." I am not sure how to get rid of this error.

Here is my code:

x = 0:.01:.65;
q=1.6022e-19;  
C=28.73;         
T=273+C;         
k=1.3806e-23;    
Is=1.0e-12;     
V= x;            
n=1;            
Vt=(k*T)/q;      

Id=Is*((exp(V/(n*Vt))));  
plot(V,Id)
axis([-0.5,0.7,-0.1,0.3])
grid on
title('I-V Characteristics of Diode')
xlabel(' Voltage ')
ylabel(' Current ')

R = diff(Vt,Id);

Answer 1

[Star Strider]

It is not clear to me what you want to do.

If you want to take the numerical derivative of ‘Id’ using step size ‘Vt’ use the gradient function as:

R = gradient(Id,Vt);

This also has the advantage that ‘R’ is the same size as ‘Id’.