[yt-users] Obtaining the current Enzo timestep from yt

[Sam Skillman]

Hi Roberto,

Unfortunately the documentation for that parameter is incorrect.  It is not
the timestep for the current step, but rather the timestep for the *first*
step. It is a way to limit the first timestep to be small, which is useful
for some problem types. I'll open an issue for this incorrect documentation.

If you are analyzing a series of outputs, it may be fairly straightforward
to calculate the dt between them using a TimeSeries object (
http://yt-project.org/doc/analyzing/time_series_analysis.html) , but I
don't know of a way to get this directly from any information that Enzo
dumps out -- same goes for yt's ability to read it in.

Sam


On Mon, Dec 2, 2013 at 4:14 PM, trobolo dinni <
trobolo.trobolo.dinni5 at gmail.com> wrote:

> Hi Sam,
>
> referring to the Enzo documentation:
>
> InitialTime (internal) The time, in code units, of the current step. For
> cosmology the units are in free-fall times at the initial epoch (see *Enzo
> Output Formats*<http://enzo.readthedocs.org/en/latest/user_guide/EnzoOutputFormat.html#enzooutputformats>).
> Default: generally 0, depending on problem Initialdt (internal) The
> timestep, in code units, for the current step. For cosmology the units are
> in free-fall times at the initial epoch (see *Enzo Output Formats*<http://enzo.readthedocs.org/en/latest/user_guide/EnzoOutputFormat.html#enzooutputformats>).
> Default: generally 0, depending on problem
> my understanding from this is that as Enzo does for the parameter
> InitialTime, also Initialdt should be saved in the parameters file and
> represents the TopGrid timestep computed by Enzo at each TopGrid cycle. So
> when during a run the console outputs for example:
> TopGrid dt = 7.815060e-05     time = 0.52042974743667    cycle = 7138
>
> the time and cycle are actually saved in the parameter file (if an output
> is scheduled for that cycle), but dt is not, while I would expect that to
> be saved to. Am I right?
> dt is the thing I need because I would like to do some data analysis that
> requires the time step (iI need to analyse the evolution of some quantities
> over a cycle).
>
> Thanks,                Roberto
>
>
> On 3 December 2013 10:43, Sam Skillman <samskillman at gmail.com> wrote:
>
>> Hi Roberto,
>>
>> InitialTime is the current timestep in the simulation.  It refers to the
>> start time of the current timestep (as opposed to an intermediate time
>> during the adaptive timestepping in Enzo).  Initialdt is not written out to
>> the output parameter files because it is only used for the very first step
>> in the simulation.
>>
>> A shortcut that currently exists is pf.current_time, which is the same as
>> pf.parameters['InitialTime'].
>>
>> I hope that helps,
>> Sam
>>
>>
>>
>> On Mon, Dec 2, 2013 at 3:36 PM, trobolo dinni <
>> trobolo.trobolo.dinni5 at gmail.com> wrote:
>>
>>> Hi Matt,
>>>
>>> yes, I don't know why it is not there.
>>>
>>> I tried with the pf.parameters function:
>>>
>>> *In [456]: pf.parameters['Initialdt']*
>>>
>>> *---------------------------------------------------------------------------*
>>> *KeyError                                  Traceback (most recent call
>>> last)*
>>>
>>> */home/cthulhu/Repository/Python/yt
>>> scripts/5.primary_damping_analysis.py
>>> <http://5.primary_damping_analysis.py> in <module>()*
>>> *----> 1 *
>>> *      2 *
>>> *      3 *
>>> *      4 *
>>> *      5 *
>>>
>>> *KeyError: 'Initialdt'*
>>>
>>>  *In [458]: pf.parameters['InitialTime']*
>>> *Out[458]: 0.52818454582493*
>>>
>>> but since Initialdt is not there it is not able to find it.
>>>
>>> Can I ask if is there a way to tell Enzo to write out the Initialdt or
>>> should be there by default?
>>>
>>> Thanks,
>>>              Roberto
>>>
>>>
>>>
>>>
>>>
>>>
>>> On 3 December 2013 10:13, Matthew Turk <matthewturk at gmail.com> wrote:
>>>
>>>> Hi Roberto,
>>>>
>>>> On Mon, Dec 2, 2013 at 6:10 PM, trobolo dinni
>>>> <trobolo.trobolo.dinni5 at gmail.com> wrote:
>>>> > Dear YT users,
>>>> >
>>>> > I would like to ask a simple question to which I was not able to find
>>>> a
>>>> > solution.
>>>> >
>>>> > My Enzo parameters file does not have any Initialdt line saved, also
>>>> if by
>>>> > reading the Enzo documentation at
>>>> > http://enzo.readthedocs.org/en/latest/parameters/initialization.htmllooks
>>>> > like the line should be there; and I would like to obtain the current
>>>> > timestep from the output using yt.
>>>> >
>>>> > I would like to ask if is there a way to do that or if there is some
>>>> > alternative solution.
>>>> >
>>>> > Thanks for the help,
>>>> >                                  Roberto
>>>>
>>>> Weird that it's not there!  yt can get the cycle number if it's not.
>>>> You can see this and other parameters by looking at pf.parameters .
>>>> You can try using the "pprint" module to make it looks nice:
>>>>
>>>> import pprint
>>>> pprint.pprint(pf.parameters)
>>>>
>>>> -Matt
>>>>
>>>> >
>>>> >
>>>> >
>>>> >
>>>> >
>>>> >
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