how to differentiate this equation

if I have this equation

theta=-2*alpha*sin(kn*pi/n)*sin(2*kn*pi*s/L+2*kn*pi*(i)/n+kn*pi/n)

how can I differenat theta(s) to theta_D and theta_DD

Answer 1

[KALYAN ACHARJYA]

syms s 
theta_D=diff(theta,s);
theta_2D=diff(theta,s,2); %or theta_2D=diff(theta_D,s);

diff

[areej abdulshaheed]

this erroer occur

Error using diff

Difference order N must be a positive integer scalar.

Error in mohammed (line 43)

theta_D=diff(theta,s)

[Walter Roberson]

diff() can only be used to differentiate symbolic expressions or symbolic functions. If you attempt to differentiate a numeric array but pass in a symbolic variable as the second parameter, or pass in anything that is not a scalar integer (such as a vector of numeric values), then you would get that error.