# Diagnostics file column names

I have a model with a poorly behaving parameter `foo`, I has a lower and upper bound set in its definitions (`<lower=..., upper=...>`) and when I look at the diagnostic file I see columns name `foo`, `p_foo`, and `g_foo`.

`foo` is the parameter `foo` on the unconstrained scale (so I can recover what’s in the output file by doing `foo * (upper - lower) + lower`, but I don’t know what `p_foo` or `g_foo` are. Is this documented somewhere?

Yes I’ve been using Stan for this long and whenever I want to work with constrained parameters I just transform them manually b/c it’s been simpler to understand what all the math is doing… I think I get it now so I’d like to use this fancy syntax more.

`p_foo` is momentum and `g_foo` is gradient. It is documented somewhere; perhaps the CmdStan manual.

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