Dynare forums

hello every body;
i was confusing in writing predetermined variable in dynare; in reference manual(page 13) we have an example with this content:

Example
The following two program snippets are strictly equivalent.
Using default Dynare timing convention:
var y, k, i;
...
model;
y = k(-1)^alpha;
k = i + (1-delta)*k(-1);
...
end;
Using the alternative timing convention:
var y, k, i;
predetermined_variables k;
...
model;
y = k^alpha;
k(+1) = i + (1-delta)*k;
...
end;

it seems i should write the predetermined variable in this format (k(+1)-k=....)
but in other page in reference manual(page 21); the author said that variables
declared as predetermined will be lagged on period back

"the timing convention of predetermined variables will have been changed to the default Dynare timing convention; in other words, variables declared as predetermined will be lagged on period back"

finally how can i write predetermined variables in dynare?
thanks for helping me.

The second statement is about Dynare's internal treatment and output. It does not affect the way you enter variables to Dynare. There, only the statement on page 13 applies.
So think about whether you use beginning or end of period stock notation and then either use the predetermined_variables command to transfer the beginning of period stock notation to Dynare's convention or use the end of period stock notation without the predetermined_variables command.

thank you very much
then i sholud write every predetermined variable in this format (k(+1)-k) in dynare

No. You have to pick the timing consistent with the timing convention you want to use. Either
1. (k(+1)-k) with predetermined_variable k;
or
2. (k-k(-1)) without the predetermined_variable command

I also do not understand why you use first differences.