# Log Linearising

Hello everyone,

I am trying to log-linearise my model and I am not quite certain how this is implemented in Dynare. Looking at my first equation:
a=e^(tau)

To my understanding, in order to log-linearise this eqation I would need to do the following:
a’(â+1)=e’^(tau)(tau*ê+1)
where:
â= log a - log a’
ê= log e - log e’
the prime indicates the steady state value

How does this translate to Dynare? Michel had written in an earlier post:

F(X_t)=0 original equation

F(exp(lx_t))=0 log-linearised

where:

lx_t = log(X_t)

According to this, I would write my equation as:

exp(ln_a)=exp(tau*ln_e)
where ln_a= log(a)

Is this correct? How does this relate to the transformation above?
If this is correct, how would I correctly define this in the model. Would this be in the initval section where I declare the ss values as ln_a=log(a)? Does this interfere with the fact that my ss values of my endogenous variables for the linear case would be all zero?

Thank you for your help,
Tartaglia

Would it makes sense to declare the initial values of all ln_x variables as = 0 instead, that is instead of saying x=0, ln_x=0?