Neural networks: How to use param in apply(n,param) and da_dn.m ?

My apply function looks something like this:

function A = apply(n,param) %.... %.... A=a1.*a2; end

now I would like to use a1 and a2 to speedup the derivative computation in da_dn.m (this has already been done with default transfer function tansig.m, but with the final value (A in my code))