[yt-users] Coexistence of positive and negative values on a SlicePlot in log scale

Nathan Goldbaum nathan12343 at gmail.com
Wed Jul 16 15:53:39 PDT 2014


On Wed, Jul 16, 2014 at 3:50 PM, Suoqing JI <suoqing at physics.ucsb.edu>
wrote:

> Hi,
>
> I understand that typically the negative values would appear as white
> color on a log slice plot. However, if I directly plot the fields that are
> generically defined in FLASH, the negative values DO appear correctly. For
> example, the velx field: http://pbrd.co/1jz3iqR.
>

Yup - that plot is on a linear scale.  I believe the FLASH frontend has it
explicitly defined *not* to log-scale velx.


>
> But for any derived fields, for example, defining velx1 = 1.*velx, the
> negative values appear white again: http://pbrd.co/1jz4oD8.
>

That happens because the default for a derived field is to log scale the
field in plots.


>
> So, is there anyway to show both positive and negative values on a log
> slice plot for derived fields (I’m using YT2)?
>
>
Nope.  In general you can't show negative values on a log-scaled plot.

You could plot the absolute value of a field but then you aren't really
plotting the field as such.

What is the visualization goal you are trying to accomplish here?


> Thanks!
>
> Best wishes,
>  --
> Suoqing JI
> Ph.D Student
> Department of Physics
> University of California, Santa Barbara
> CA 93106, USA
>
>
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