The way you can do this with so many predictor variables and coefficients is to vectorize the equation. Then you just have to be consistent about how you vectorized. For your case, we could do the following:
This means that X would be a big matrix where each column is one of your predictor variables. For there, you have to be careful with multiplication, division, and exponentiation to ensure they are element-wise operations.
For example, to compute this
you need to execute the following in modelfun(b,x):
(x(:,4)./x(:,5)).^b(7)
