[visit-users] Plotting questions - changing axes and expressions

Mark Miller miller86 at llnl.gov
Tue Mar 30 16:35:50 EDT 2010

On Tue, 2010-03-30 at 16:23 -0400, Brandt Belson wrote:
> Hello,
> I have  a few questions I haven't been able to figure out after
> reading the documentation. 
> First, I'd like to essentially crop a plot. I have a 3D domain that is
> much longer in the x-direction than y and z, and I'd like to look at
> only a specific range in x. I can use the clip or box operators to
> remove the portions of the plot I'm not interested in, but I further
> want visit to resize the bounding box to include only the shortened
> range in x. As it is, I can't remove the very long domain in x which
> makes every further operation more difficult.

VisIt has the option of deriving its view parameters from 'original'
data or 'actual' data. Original is as the database VisIt is reading
defines it. Actual is as the data you are currently plotting has it. So,
go to Options->View. Select Advanced Tab, Set 'view based on 'actual'

> I'd also like to do two tasks with expressions. I'd like to compute
> the vorticity from the three components of velocity (in a fluid flow).
> I'm only interested in the x-component of vorticity, but I do not see
> a way to take partial derivatives in only one direction in
> expressions. Is this possible, or do I need to use the curl function
> then look at the x component as a scalar field? It seems like that
> would be computationally wasteful.

So, are your datasets so big that the 'wasteful'ness of this approach
really, really hurts? If so, then I think maybe a hand-tuned expression
defined using the most primitive building blocks we have might be able
to get it but perhaps at the expense of too many 'intermediate' terms in
our expression system to be of any great use. Otherwise, yes, it is
wasteful for your use case but I can't think if a 'better' route to
visualize what you're after.

> I'd also like to average a scalar field over the entire z-dimension,
> leaving only a 2D plot in x and y.

I think that is possible. Let me give this some thought and get back to

> Thank you
> --
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Mark C. Miller, Lawrence Livermore National Laboratory
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