# A few questions about dynare code?

Dear Professor Pfeifer，

I have been learning Dynare for some time and I encountered a few questions when writing the dynare code. Would you please help me out ? Any reply will be appreciated, thank you !

(1) It’s a question about the form of shock equation. In a non-linear model, when the code is written like “exp(var)” form, the shock equation is written as:
“exp(A_e) = 1 - rho_A_e * 1 + rho_A_e * exp(A_e(-1)) + e_A_e”,
but if the code is written like “var” form(without “exp” ), Does the shock equation should be written as:
“A_e = 1 - rho_A_e * 1 + rho_A_e * A_e(-1) + e_A_e” ?

(2) It’s also a question about shock equation. In a non-linear model, when the code is written like “var” form, Is there any chance that the shock equation is written as:
“log(A_e) = rho_A_e * log (A_e(-1)) + e_A_e” ?

(3) It’s a question about Bayesian estimation. Is there a normal range of the " initial value of the log posterior(or likelihood)" so that I could tell whether the code is right or not from the beginning of the estimation ?

Any reply will be appreciated, thanks again !

1. Yes, the two specifications are consistent and can be used.
2. That depends on how `A_e` enters the other model equations. It is common to have
``````Y=A*K^alpha*L^(1-alpha)
log(A)=rho_A*log (A(-1)) + e_A
``````
1. That depends very much on the data you use, but anything too big in absolute value, say bigger than 1e7 is highly suspicious.

Dear Professor Pfeifer，

Happy New Year and thank you for your reply, that helps a lot.

But as you said that it is common to have

‘‘Y=AK^alphaL^(1-alpha)
log(A)=rho_A*log (A(-1)) + e_A’’

Could the shock equation be written as:
“A = 1 - rho_A * 1 + rho_A * A(-1) + e_A”
in this situation ?

At `order=1` the two specifications are identical.