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Francois Maltey, on 2011-02-02 15:51, wrote:

Hello,

I use matplolib by the mathematical system Sage in order to plot a function.

The Sage code calls matplotlib and uses its options : The Sage command is

plot (sin, x, -5, 5)

I add labels par axes_labels or remove axes by :

plot (sin(x), x, -5, 5, axes_label = ['x', 'y'])

plot (sin(x), x, -5, 5, axes=false)

French users (and maybe others) uses arrows and not lines for axes.

I'm looking for a plot (sin(x), x, -5, 5, axes="arrows")

Is there a pretty way to get these arrows. The result of this code isn't

so fine.

length, width and color don't match.

plot (sin(x), x, -5, 5, axes=false) + arrow ((-5,0),(5,0)) + arrow

((0,-1),(0,1))

What options do you propose ?

I don't find relevant answers in the archive.

Hi Francois,

I'm not sure I understand - but do you want the arrows at the end

of the axes spines? I don't think there's a direct way to adjust

the spines to become arrows at the moment, but we can remedy that

by making annotations in axes coordinates. The important thing

to know here is that in axes coordinates, which are always

between 0-1, spine endpoints are at these locations: (0,0),

(0,1), (1,0), and (1,1). Here's the code, and attached is the

resulting image

import matplotlib.pyplot as plt

ax = plt.subplot(1,1,1)

al = 7 # arrow length in points

arrowprops=dict(clip_on=False, # plotting outside axes on purpose

frac=1., # make end arrowhead the whole size of arrow

headwidth=al, # in points

facecolor='k')

kwargs = dict(

xycoords='axes fraction',

textcoords='offset points',

arrowprops= arrowprops,

)

ax.annotate("",(1,0),xytext=(-al,0), **kwargs) # bottom spine arrow

ax.annotate("",(0,1),xytext=(0,-al), **kwargs) # left spin arrow

# hide the top and right spines

[sp.set_visible(False) for sp in ax.spines['top'],ax.spines['right']]

#hide the right and top tick marks

ax.yaxis.tick_left()

ax.xaxis.tick_bottom()

x = np.linspace(-5,5,50)

ax.plot(x, np.sin(x))

# adjust the view a little bit

ax.set_xlim(-5,5)

ax.set_ylim(-1.1,1.1)

plt.draw()

I'm not familiar with how SAGE exposes matplotlib functionality,

though, since the syntax you used differs from how matplotlib is

utilized.

best,

## ···

From: Paul Ivanov <pivanov314@...287...>

To: Francois Maltey <fmaltey@...3425...>

Subject: Re: [Matplotlib-users] Is it possible to plot axes with arrows ?

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Paul Ivanov

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