matplotlib-users Mailing List for matplotlib

per freem wrote:
> hi all,
> 
> I am plotting certain dashed lines in matplotlib, using:
> 
> plt.plot(x, y, '--')
> 
> I'd like to set the dash size (i.e. length of each dash) and the gap
> between the dashes of the plotted line. Is there a way to set this
> from matplotlib?

plt.plot([0,1], [2,3], '--', dashes=(10,20))

The dashes kwarg sets a Line2D parameter. See
http://matplotlib.sourceforge.net/api/artist_api.html#matplotlib.lines.Line2D.set_dashes

Eric

> 
> thanks.
> 
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hi all,

I am plotting certain dashed lines in matplotlib, using:

plt.plot(x, y, '--')

I'd like to set the dash size (i.e. length of each dash) and the gap
between the dashes of the plotted line. Is there a way to set this
from matplotlib?

thanks.

Moving to the devel list, since this concerns an internal API of
matplotlib. Thanks to Sourav for reporting this and to Eric for sending
the note to me.

Eric Firing <ef...@ha...> writes:

> Sourav K. Mandal wrote:
>> I have a simple problem: when outputting to PDF or SVG, alpha blending
>> does not work for the lines drawn by "contour".  However, alpha blending
>> does work for the regions given by "contourf".  
>
> You are right, this is a real bug, verified in svn.  

The contour function creates a LineCollection, which gets drawn via
draw_path_collection, which the pdf backend inherits from backend_bases.
The default draw_path_collection (or _iter_collection really)
communicates the alpha of the *face color* only by setting the alpha
attribute of the GraphicsContext:

            if rgbFace is not None and len(rgbFace)==4:
                gc0.set_alpha(rgbFace[-1])
                rgbFace = rgbFace[:3]

The alpha of the line only gets communicated via the fourth component of
the rgb attribute of the GraphicsContext, and currently the pdf backend
doesn't do anything with it.

I think this could be resolved in a number of ways, none of which is
obviously the perfect solution:

1. Add a check in _iter_collection for gc0._rgb having an alpha
   component, similar to the current check for rgbFace, and set the
   alpha attribute from that one too. (What if both rgbFace and gc0._rgb
   have an alpha component?)

2. Make each backend's GraphicsContext set the alpha attribute from the
   color. (If the alpha attribute is already set, how should they be
   combined? Multiply, take the minimum, or what?)

3. Either get rid of the alpha attribute on the GraphicsContext and use
   only rgba tuples within backends, or turn it into two attributes
   (e.g. alphaFace and alphaStroke). (What to do with the frontend's
   single alpha attribute?)

By the way, I have never really understood why rgbFace is given
separately from the GraphicsContext. Is this just an evolutionary
remnant or is there a deeper meaning for it?

-- 
Jouni K. Seppänen
http://www.iki.fi/jks

Am Freitag, 29. Januar 2010 21:00:04 schrieb Sebastian Busch:
> Florian Lindner wrote:
> > Hello,
> > 
> > I try to use LaTeX in my plot....
> > 
> > florian@horus:~> cat .matplotlib/matplotlibrc
> > text.usetex        : true
> > 
> > My plotting code looks like:
> > 
> > Ma = arange(1.0, 5.0, 0.01)
> > Ts = [T(i) for i in Ma]  # BTW: Is there a way to spare this line?
> not sure what T is. you could try T(Ma); you can do that of course also
> directly in the plot command

T is a python function:

def T(Ma):
    fp = fluidproperties.IdealGas()
    fp.Ma = Ma
    return NormalShock(fp).fp_out().T / fp.

plot(Ma, T(Ma), label=r'$\frac{T2}{T1}$') does not work. The plot window appears, but no plot.

> > plot(Ma, Ts, label=r'/frac{T2}{T1}')
> should be backslash and math mode:

> plot(Ma, Ts, label=r'$\frac{T2}{T1}$')
> legend()
> show()
> 
> > and that's all, no plot window appears, the script is finished.
> 
> you did not show() !

Actually I did it. I stripped the code before pasting it here, my fault. But not it works, thanks!

Florian

Hi

I am using "verts" in the matplotlib scatter function and managed to
create many new symbols for scatter plots. One I cannot make is a
spiral-like symbol (logarithmic spiral) because it does connect the
first and last point of the verts series of x,y points I am defining. Is
there a way to avoid that? (so that the spiral-curve stays "open")

thanks!

Eric