Working with arrows

Community matplotlib-users
1

Hello,
I'm trying to use arrows but I'm a little stuck.

In [1]: import matplotlib

In [2]: matplotlib.__version__
Out[2]: '0.98.5.3'

First, simply

import matplotlib.pyplot as plt
plt.arrow(2,2,4,1)

doesn't show anything, while at least a figure with an arrow in is
expected (or it's by design?)

Secondly, with this simple script:

import matplotlib.pyplot as plt
plt.plot(range(10))
plt.arrow(2,2,4,1, linewidth=5)
plt.arrow(3,3,1,4)

the result is quite ugly :slight_smile: Where is the arrow pointer (for example)?

I hope I'm missing something, but even in examples like "usetex_demo"
the arrows are drawn "by hand" :slight_smile:

Thanks,

mpl_arrowspng.png

···

--
Sandro Tosi (aka morph, morpheus, matrixhasu)
My website: http://matrixhasu.altervista.org/
Me at Debian: http://wiki.debian.org/SandroTosi

2

You need to adjust the keyword arguments, such as head_width, etc. The
arrow command itself is poorly documented and its keyword arguments
are explained in
matplitlib.patches.FancyArrow. However, I recommend you to use
annotate command instead of arrow (you can give empty string if you
just need an arrow). For example,

annotate("", (0.2, 0.2), (0.4, 0.4),
               arrowprops=dict(arrowstyle="->"))

more examples,

http://matplotlib.sourceforge.net/examples/pylab_examples/annotation_demo.html
http://matplotlib.sourceforge.net/examples/pylab_examples/annotation_demo2.html

Annotate does not adjust the xlim and ylim of your axes for you, thus
it is your responsibility.

-JJ

···

On Wed, Mar 25, 2009 at 6:39 PM, Sandro Tosi <morph@...10...> wrote:

Hello,
I'm trying to use arrows but I'm a little stuck.

In [1]: import matplotlib

In [2]: matplotlib.__version__
Out[2]: '0.98.5.3'

First, simply

import matplotlib.pyplot as plt
plt.arrow(2,2,4,1)

doesn't show anything, while at least a figure with an arrow in is
expected (or it's by design?)

Secondly, with this simple script:

import matplotlib.pyplot as plt
plt.plot(range(10))
plt.arrow(2,2,4,1, linewidth=5)
plt.arrow(3,3,1,4)

the result is quite ugly :slight_smile: Where is the arrow pointer (for example)?

I hope I'm missing something, but even in examples like "usetex_demo"
the arrows are drawn "by hand" :slight_smile:

Thanks,
--
Sandro Tosi (aka morph, morpheus, matrixhasu)
My website: http://matrixhasu.altervista.org/
Me at Debian: http://wiki.debian.org/SandroTosi

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3

Hi Jae-Joon,
thanks for the reply.

You need to adjust the keyword arguments, such as head_width, etc. The

But shouldn't the default arrow be a little bit "nicer" than it's now? :slight_smile:

arrow command itself is poorly documented and its keyword arguments
are explained in
matplitlib.patches.FancyArrow.

Ah, that's why even in pyploy.arrow() I could'nt find eny reference to
head_width & friends. In case I have some time to share on improve
arrow() docs, what docs should I look to? and changing
'doc/api/pyplot_api.rst' is the right place to achieve it?

However, I recommend you to use
annotate command instead of arrow (you can give empty string if you
just need an arrow). For example,

annotate("", (0.2, 0.2), (0.4, 0.4),
arrowprops=dict(arrowstyle="->"))

more examples,

http://matplotlib.sourceforge.net/examples/pylab_examples/annotation_demo.html
http://matplotlib.sourceforge.net/examples/pylab_examples/annotation_demo2.html

I already treated annotation, but I would like to give the readers (of
the book) a much wider toolbox, so introducing bare arrows after
annotations seems straigthforward.

Annotate does not adjust the xlim and ylim of your axes for you, thus
it is your responsibility.

Yep, already noticed :smiley:

Cheers,

···

On Thu, Mar 26, 2009 at 02:51, Jae-Joon Lee <lee.j.joon@...287...> wrote:
--
Sandro Tosi (aka morph, morpheus, matrixhasu)
My website: http://matrixhasu.altervista.org/
Me at Debian: http://wiki.debian.org/SandroTosi

4

Have you seen the arrow and fancy arrow demos

http://matplotlib.sourceforge.net/examples/pylab_examples/arrow_demo.html

http://matplotlib.sourceforge.net/examples/pylab_examples/fancyarrow_demo.html

Both of these use older and less sophisticated arrows that JJ’s FancyArrowPatch

http://matplotlib.sourceforge.net/api/artist_api.html?highlight=fancyarrowpatch#matplotlib.patches.FancyArrowPatch

so perhaps the best thing for you to do would be to write an example using the FancyArrowPatch directly.

JDH

···

On Thu, Mar 26, 2009 at 9:59 AM, Sandro Tosi <morph@…10…> wrote:

Hi Jae-Joon,

thanks for the reply.

On Thu, Mar 26, 2009 at 02:51, Jae-Joon Lee <lee.j.joon@…287…> wrote:

You need to adjust the keyword arguments, such as head_width, etc. The

But shouldn’t the default arrow be a little bit “nicer” than it’s now? :slight_smile:

arrow command itself is poorly documented and its keyword arguments

are explained in

matplitlib.patches.FancyArrow.

Ah, that’s why even in pyploy.arrow() I could’nt find eny reference to

head_width & friends. In case I have some time to share on improve

arrow() docs, what docs should I look to? and changing

‘doc/api/pyplot_api.rst’ is the right place to achieve it?

However, I recommend you to use

annotate command instead of arrow (you can give empty string if you

just need an arrow). For example,

annotate(“”, (0.2, 0.2), (0.4, 0.4),

          arrowprops=dict(arrowstyle="->"))

more examples,

http://matplotlib.sourceforge.net/examples/pylab_examples/annotation_demo.html

http://matplotlib.sourceforge.net/examples/pylab_examples/annotation_demo2.html

I already treated annotation, but I would like to give the readers (of

the book) a much wider toolbox, so introducing bare arrows after

annotations seems straigthforward.