Question about inputs in model setup

I have got some rate of infusion stored in a vector and i convolve that 
directly with impulse response to get the concentration input.

c(t) = x(t) * f(theta,t);//x = known infusion vector, f = parameterised 
impulse reponse where theta needs to be estimated.

How would i specify this in my model setup.

Thank you in advance. Any help will be much appreciated.

Ipsita