Re: [Matplotlib-users] Input array dimensions for contour or contourf

[Benjamin R. <ben...@ou...>]

On Tue, May 31, 2011 at 1:28 PM, Eric Firing <ef...@ha...> wrote:

> On 05/31/2011 08:03 AM, Benjamin Root wrote:
>
>>
>>
>> On Tue, May 31, 2011 at 12:58 PM, Eric Firing <ef...@ha...
>> <mailto:ef...@ha...>> wrote:
>>
>>    On 05/31/2011 05:50 AM, Benjamin Root wrote:
>>     >
>>     >
>>     > On Tue, May 31, 2011 at 10:34 AM, Mannucci, Anthony J (335G)
>>     > <ant...@jp...
>>    <mailto:ant...@jp...>
>>     > <mailto:ant...@jp...
>>    <mailto:ant...@jp...>>> wrote:
>>     >
>>     >     The following program seems to work with contour/contourf.
>>    However
>>     >     the documentation for the contourf function states
>>     >
>>     >     contour(X,Y,Z)
>>     >
>>     > "/X/, /Y/, and /Z/ must be arrays with the same dimensions."
>>     >
>>     >     I am finding that contour works if the dimension of X and Y
>>    are 1,
>>     >     but Z must be two-dimensional. The following program seems to
>>    bear
>>     >     this out. Are the arrays x and y below two-dimensional, or is
>> the
>>     >     documentation misleading? Thanks for your help.
>>     >
>>     >     import numpy as N
>>     >     import pylab as PLT
>>     >
>>     >     lons = N.linspace(-5.,5.,5) # Is this a one or two
>>    dimensional array?
>>     >     lats = N.linspace(-3.,3.,4)
>>     >
>>     >     z = N.zeros((len(lats), len(lons)))
>>     >     for i in range(len(lons)):
>>     >          for j in range(len(lats)):
>>     >              z[j,i]=i+j
>>     >
>>     >     PLT.clf()
>>     >     PLT.contourf(lons,lats,z)
>>     >     PLT.colorbar()
>>     >     PLT.show()
>>     >
>>     >     -Tony
>>     >
>>     >
>>     > Tony,
>>     >
>>     > contour and contourf seems to take advantage of numpy's broadcasting
>>     > feature, so it is probably more correct to say that X and Y must
>>    be at
>>     > least broadcastable to the shape of Z.  I think there are a number
>> of
>>
>>    Not quite; if x and y are 1-D, meshgrid is called to make 2-D versions,
>>    which must then match Z. Broadcasting is not used or supported. So, the
>>    contour docstring was not updated when this functionality was added,
>>    long ago.  Consider it an undocumented feature, in need of
>>    documentation.
>>
>>    Eric
>>
>>
>> Well, (as a bit of a cop-out) in my edit, I didn't say that they were
>> broadcasted, only that they must be broadcastable to the same shape.
>> Would that suffice, or should I re-word that?
>>
>
> It would not be correct.
>
> x and y must both be 2-D, with the same shape as z; or they must both be
> 1-D such that len(x) is the number of columns in z and len(y) is the number
> of rows.
>
> Eric
>
>
Gotcha, I didn't think about the mixed 1-D and 2-D case.

In addition, is the note in the contour doc about masked arrays still valid,
or can this be removed/updated?

"*Z* may be a masked array, but filled contouring may not handle internal
masked regions correctly."

Ben Root