[ADMB Users] dvariable vs. prevariable

[James Thorson]

Hi all,

I had a quick coding question that I couldn't answer online.  What is the difference between dvariables and prevariables?  They seem to be used interchangably in calls to SEPARABLE_FUNCTIONS, and it appears that dvariables are defined based on prevariables.  Is one faster to use than the other, or more appropriate for particular uses?

Seems like a useful question to have documented on the redmine (where I understand, perhaps mistakenly, that any answers to this inquiry will be stored)..

Cheers,

Jim

[dave fournier]

prevariable is better for separable_functions.

The difference is between say x(i) when x is a dvar_vector. then x(i) is a prevariable.
If you pass x(i) to a function which takes a dvariable a constructor is invoked to change
it to a dvariable. This incurs a bit of overhead. Also if you changed the value of argument
corresponding to x(i) inside the function the original x(i) would not be changed
since you are actually changing a different object.

If this seems bizarre it was done so that
the access functions x(i) and x[i] which involve a copy
constructor would not incur extra overhead.




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