[Matplotlib-users] Query about streamplot

[vincent.adrien at gmail.com]

Kumar,

As far as I understand it, it looks like your issue may be due to X (and
possibly Y) being 2d-array. If V and Omega are arrays with shape **(Ny,
Nx)**, then X and Y should be **1d-arrays** with Nx and Ny elements
respectively. For simplicity sake (I guess), there is actually a special
(not very well documented) case if X and Y are 2d-arrays :
- each row of X has to be the same;
- each column in Y has to be same.

The error that you saw suggest that the rows in your array X differ from
one another.

Adrien

Le 17/04/2019 à 11:55, Dhirendra Kumar a écrit :
> Hii Adrien
> 
> Thanks for the reply. I have tried your example and could replicate it.
> But in case of my script I have two variables:
> 
> *V* and *Omega* having sizes:
> ([('plev', 12), ('lat', 81)]))
> ([('plev', 12), ('lat', 81)]))
> 
> Plev has to be plotted on y axis and lat has to be plotted on x axis. 
> 
> I am using following lines to create the plot:
> 
> plt.subplot(331)
> plt.contourf(CC_W_CON11,cmap='RdBu')
> plt.streamplot(X, Y, Omega,  V)
> 
> This gives me an error as:
> 
>   File
> "/opt/apps/ANACONDA/lib/python3.7/site-packages/matplotlib/pyplot.py",
> line 2951, in streamplot
>     if data is not None else {}))
>   File
> "/opt/apps/ANACONDA/lib/python3.7/site-packages/matplotlib/__init__.py",
> line 1810, in inner
>     return func(ax, *args, **kwargs)
>   File
> "/opt/apps/ANACONDA/lib/python3.7/site-packages/matplotlib/axes/_axes.py",
> line 4882, in streamplot
>     integration_direction=integration_direction)
>   File
> "/opt/apps/ANACONDA/lib/python3.7/site-packages/matplotlib/streamplot.py",
> line 79, in streamplot
>     grid = Grid(x, y)
>   File
> "/opt/apps/ANACONDA/lib/python3.7/site-packages/matplotlib/streamplot.py",
> line 311, in __init__
>     raise ValueError("The rows of 'x' must be equal")
> *ValueError: The rows of 'x' must be equal*
> *
> *
> Could you please look if there is any mistake ??
> 
> Thanks
> 
> 
> On Wed, Apr 17, 2019 at 1:27 PM vincent.adrien at gmail.com
> <mailto:vincent.adrien at gmail.com> <vincent.adrien at gmail.com
> <mailto:vincent.adrien at gmail.com>> wrote:
> 
>     Kumar,
> 
>     FWIW, based on the [streamplot
>     example](https://matplotlib.org/gallery/images_contours_and_fields/plot_streamplot.html)
>     in the gallery, the following snippet seems to be working just fine
>     (with Matplotlib 3.0.1) “even though” the amount of X and Y coordinate
>     values is (Nx, Ny) = (100, 50).
> 
>     ```python
>     import numpy as np
>     import matplotlib.pyplot as plt
> 
>     # Dummy data
>     w = 3
>     Nx, Ny = 100, 50
>     Y, X = np.mgrid[-w:w:50j, -w:w:100j]
>     U = -1 - X**2 + Y
>     V = 1 + X - Y**2
> 
>     fig, ax = plt.subplots()
> 
>     ax.streamplot(X, Y, U, V)
>     ax.set_title(f"{Nx/Ny:g}× more points along X than Y")
>     ```
> 
>     Best,
>     Adrien
> 
>     Le 17/04/2019 à 08:14, Adrien VINCENT a écrit :
>     > Hi Kumar,
>     >
>     > Could provided a snippet with a (standalone) minimal working
>     example of what you have tried ?
>     >
>     > AFAICT, looking at
>     https://matplotlib.org/api/_as_gen/matplotlib.axes.Axes.streamplot.html
>     it does not look like X and Y arrays of coordinates have to be of
>     equal length (but the velocity arrays U and V should have relevant
>     dimensions relative to X and Y).
>     >
>     > Best regards,
>     > Adrien
>     >
>     >
>     >
>     > On April 16, 2019 11:05:01 PM GMT+02:00, Dhirendra Kumar
>     <dhirendra.cub at gmail.com <mailto:dhirendra.cub at gmail.com>> wrote:
>     >> Hii Folks
>     >>
>     >> I have an array with dimension (plev: 7, lat: 81). I was trying
>     to draw
>     >> streamline plot for Omega and V wind [Hadley cell].  I am facing some
>     >> error
>     >> with* plt.streamplot* as it says that both the dimension should be of
>     >> equal
>     >> size (i.e. N * N ). Is there any other way to create a streamline
>     plot
>     >> for
>     >> the data having unequal values along both the dimensions?
>     >>
>     >> I seek help of the community in this regard.
>     >>
>     >> I hope I framed my question correctly.  Please let me know if I
>     need to
>     >> clarify more details.
>     >>
>     >> Thank you
>     >
> 
> 
> 
> -- 
> ========================================
> Dhirendra Kumar
> PhD Student
> School of Environmental Sciences, JNU
> New Delhi (India)
> Contact: +91 9910778043
> Alternate email: dhirendra.cub at outlook.com
> <mailto:dhirendra.cub at outlook.com>
> =========================================