[Matplotlib-users] Query about streamplot

Wed Apr 17 14:58:48 EDT 2019

Hii Adrien

I guess I have found the problem but don't know how to go about it. The
documentation here (
https://matplotlib.org/api/_as_gen/matplotlib.pyplot.streamplot.html) says
that  x and y should be:

*x*, *y* : 1d arraysan *evenly spaced* grid.but in my case although I have
the same shape of the V and Omega values, it is unevenly distributed as a
grid. The plev values are: [1000.  925.  850.  700.  600.  500.  400.
300.  250.  200.  150.  100.] while x varies from 0-40 N at an interval of
0.5. So apparently it produces an unevely distributed gridspace in lat-plev
(xy).Please let me know what you think about this.ThanksDhirendra

On Wed, Apr 17, 2019 at 7:51 PM vincent.adrien at gmail.com <
vincent.adrien at gmail.com> wrote:

> 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>
> > =========================================
>
>

-- 
========================================
Dhirendra Kumar
PhD Student
School of Environmental Sciences, JNU
New Delhi (India)
Contact: +91 9910778043
Alternate email: dhirendra.cub at outlook.com
=========================================
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