This looks like it would be a welcome addition to the code if someone wants to put it together, but I agree, that at the minimum, we should remove the bad index value returned to the user. Good idea! On Mon, Nov 23, 2015 at 1:08 PM, Matthew Turk wrote:

I have an alternate solution to this problem, which dovetails with the numpy-like operations.

If we were to make a different DerivedQuantity (which MaxLocation and MinLocation could subclass with a prescription that they return x,y,z) that accepted the names of the fields to obtain at the maximum value of a field, this could probably accomplish what you are looking for. This would be equivalent to the .argmax() operation, so you would be able to do:

dd = ds.all_data() dd.argmax("density", ["temperature", "velocity_magnitude"])

and get back the temperature and velocity_magnitude fields at the maximum density.

Would that suffice?

On Sun, Nov 22, 2015 at 4:11 PM, Matthew Turk wrote:

...

I'm not sure that, as it stands, it is possible to get the "index", unless we made the parallel iteration sequential. Perhaps a better solution would be to not return the index value.

On Sun, Nov 22, 2015 at 4:06 PM, Cameron Hummels wrote:

...

New issue 1147: Derived quantities `max_location` and `min_location` not returning correct index values

https://bitbucket.org/yt_analysis/yt/issues/1147/derived-quantities-max_loca...

...

Cameron Hummels:

Something is going awry in the `max_location` and `min_location`

derived quantities such that they return an incorrect index for where the extrema occur. Here's an example script. I tried correcting the code, but I got caught up in the chunk processing for derived quantities.

...

``` #!python

import yt import numpy as np

ds = yt.load('IsolatedGalaxy/galaxy0030/galaxy0030') ad = ds.all_data() val, index, x, y, z = ad.quantities.max_location('density') print val == ad['density'][int(index)] # false

val2 = ad['density'].max() index2 = np.argmax(ad['density']) print val2 == ad['density'][index2] # true

print val == val2 # true print index == index2 # false

# Thus, something is going awry in the max_location (and the

min_location)

...

# derived quantities where it calculates the index values for the extrema ```

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