MATLAB: Error message for calculating the variance of the beta

Question

I want to calculate the variance of my beta, I am typing in this command, however i am getting the error message 'subscript indices must either be real positive integers or logical', 'Attempted to access (0.0686532); index must be a positive integer or logical'

My command is

var(b)=inv(xcl'*xcl)sqrt(sigma_r)

Answer 1

You don't make assignments like this in MATLAB

 var(b) = sqrt(2);

For example, this will produce the error you observe:

 b = randn(100,1);
 var(b) = sqrt(2);

To calculate the variance of your beta, create a variable:

 varbeta = inv(xcl'*xcl)*sqrt(sigma_r);