Thread: [Matplotlib-users] quiver without any scaling

Hi,

I woud like to draw a vector field using pylab.
quivert looks nice but it sould not scale the arrows to fit my use-case.
quiver([1],[1],[1.2],[1.2]) does plot a nice arrow but the head of the 
arrow is not at (1.2,1.2).
Is there a way to plot a list of arrows *without* any scaling?

Xavier

Hi Xavier,

You can pass some handy keyword arguments to fix that. Use the following:

quiver([1],[1],[1.2],[1.2], angles='xy', scale_units='xy', scale=1)

Hope that helps :)


Regards,
-- Damon

--------------------------
Damon McDougall
Mathematics Institute
University of Warwick
Coventry
CV4 7AL
d.m...@wa...

On 22 Nov 2009, at 16:37, Xavier Gnata wrote:

> Hi,
> 
> I woud like to draw a vector field using pylab.
> quivert looks nice but it sould not scale the arrows to fit my use-case.
> quiver([1],[1],[1.2],[1.2]) does plot a nice arrow but the head of the 
> arrow is not at (1.2,1.2).
> Is there a way to plot a list of arrows *without* any scaling?
> 
> Xavier
> 
> ------------------------------------------------------------------------------
> Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day 
> trial. Simplify your report design, integration and deployment - and focus on 
> what you do best, core application coding. Discover what's new with
> Crystal Reports now.  http://p.sf.net/sfu/bobj-july
> _______________________________________________
> Matplotlib-users mailing list
> Mat...@li...
> https://lists.sourceforge.net/lists/listinfo/matplotlib-users

Hi,

RTFM...indeed it works.
However, the axis do not scale accordingly:

quiver([1],[1],[2],[2], angles='xy', scale_units='xy', scale=1) on a 
TkAgg backend produce a plot with:
In [11]: axis()
Out[11]:
(0.94000000000000006,
  1.0600000000000001,
  0.94000000000000006,
  1.0600000000000001)

The display area scales the same way as it does using 
quiver([1],[1],[2],[2]) (without any other args).
It looks like a bug.

Xavier


> Hi Xavier,
>
> You can pass some handy keyword arguments to fix that. Use the following:
>
> quiver([1],[1],[1.2],[1.2], angles='xy', scale_units='xy', scale=1)
>
> Hope that helps :)
>
>
> Regards,
> -- Damon
>
> --------------------------
> Damon McDougall
> Mathematics Institute
> University of Warwick
> Coventry
> CV4 7AL
> d.m...@wa...
>
> On 22 Nov 2009, at 16:37, Xavier Gnata wrote:
>
>    
>> Hi,
>>
>> I woud like to draw a vector field using pylab.
>> quivert looks nice but it sould not scale the arrows to fit my use-case.
>> quiver([1],[1],[1.2],[1.2]) does plot a nice arrow but the head of the
>> arrow is not at (1.2,1.2).
>> Is there a way to plot a list of arrows *without* any scaling?
>>
>> Xavier
>>
>> ------------------------------------------------------------------------------
>> Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day
>> trial. Simplify your report design, integration and deployment - and focus on
>> what you do best, core application coding. Discover what's new with
>> Crystal Reports now.  http://p.sf.net/sfu/bobj-july
>> _______________________________________________
>> Matplotlib-users mailing list
>> Mat...@li...
>> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>>      
>    

Hi Xavier (cc list),

It may be a bug, however I do not know what the default behaviour 'should' be. You could do:

lims = [-4, 4, -4, 4]
axis(lims)

after calling quiver to see the whole arrow. I did notice that calling

axis('tight')

threw the following error

/Users/Damon/python/lib/matplotlib/axes.py:2038: UserWarning: Attempting to set identical xmin==xmax results in singular transformations; automatically expanding.  xmin=1.0, xmax=1.0
  warnings.warn('Attempting to set identical xmin==xmax results in singular transformations; automatically expanding.  xmin=%s, xmax=%s'%(xmin, xmax))
/Users/Damon/python/lib/matplotlib/axes.py:2212: UserWarning: Attempting to set identical ymin==ymax results in singular transformations; automatically expanding.  ymin=1.0, ymax=1.0
  warnings.warn('Attempting to set identical ymin==ymax results in singular transformations; automatically expanding.  ymin=%s, ymax=%s'%(ymin, ymax))

is this correct, or is it a bug? I'm using "ipython -pylab" with the MacOSX backend. I was expecting axis('tight') would scale the axes so I could see the whole arrow.


Regards,
-- Damon

--------------------------
Damon McDougall
Mathematics Institute
University of Warwick
Coventry
CV4 7AL
d.m...@wa...

On 22 Nov 2009, at 21:34, Xavier Gnata wrote:

> Hi,
> 
> RTFM...indeed it works.
> However, the axis do not scale accordingly:
> 
> quiver([1],[1],[2],[2], angles='xy', scale_units='xy', scale=1) on a TkAgg backend produce a plot with:
> In [11]: axis()
> Out[11]:
> (0.94000000000000006,
> 1.0600000000000001,
> 0.94000000000000006,
> 1.0600000000000001)
> 
> The display area scales the same way as it does using quiver([1],[1],[2],[2]) (without any other args).
> It looks like a bug.
> 
> Xavier
> 
> 
>> Hi Xavier,
>> 
>> You can pass some handy keyword arguments to fix that. Use the following:
>> 
>> quiver([1],[1],[1.2],[1.2], angles='xy', scale_units='xy', scale=1)
>> 
>> Hope that helps :)
>> 
>> 
>> Regards,
>> -- Damon
>> 
>> --------------------------
>> Damon McDougall
>> Mathematics Institute
>> University of Warwick
>> Coventry
>> CV4 7AL
>> d.m...@wa...
>> 
>> On 22 Nov 2009, at 16:37, Xavier Gnata wrote:
>> 
>>   
>>> Hi,
>>> 
>>> I woud like to draw a vector field using pylab.
>>> quivert looks nice but it sould not scale the arrows to fit my use-case.
>>> quiver([1],[1],[1.2],[1.2]) does plot a nice arrow but the head of the
>>> arrow is not at (1.2,1.2).
>>> Is there a way to plot a list of arrows *without* any scaling?
>>> 
>>> Xavier
>>> 
>>> ------------------------------------------------------------------------------
>>> Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day
>>> trial. Simplify your report design, integration and deployment - and focus on
>>> what you do best, core application coding. Discover what's new with
>>> Crystal Reports now.  http://p.sf.net/sfu/bobj-july
>>> _______________________________________________
>>> Matplotlib-users mailing list
>>> Mat...@li...
>>> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>>>     
>>   
> 

Hi,

Well when you plot, imshow or whatever is matplotlib related, the axes 
do scale *automatically*.
Why should it be different with quiver?

I do reproduce your error with axis('tight')


Xavier

> Hi Xavier (cc list),
>
> It may be a bug, however I do not know what the default behaviour 'should' be. You could do:
>
> lims = [-4, 4, -4, 4]
> axis(lims)
>
> after calling quiver to see the whole arrow. I did notice that calling
>
> axis('tight')
>
> threw the following error
>
> /Users/Damon/python/lib/matplotlib/axes.py:2038: UserWarning: Attempting to set identical xmin==xmax results in singular transformations; automatically expanding.  xmin=1.0, xmax=1.0
>    warnings.warn('Attempting to set identical xmin==xmax results in singular transformations; automatically expanding.  xmin=%s, xmax=%s'%(xmin, xmax))
> /Users/Damon/python/lib/matplotlib/axes.py:2212: UserWarning: Attempting to set identical ymin==ymax results in singular transformations; automatically expanding.  ymin=1.0, ymax=1.0
>    warnings.warn('Attempting to set identical ymin==ymax results in singular transformations; automatically expanding.  ymin=%s, ymax=%s'%(ymin, ymax))
>
> is this correct, or is it a bug? I'm using "ipython -pylab" with the MacOSX backend. I was expecting axis('tight') would scale the axes so I could see the whole arrow.
>
>
> Regards,
> -- Damon
>
> --------------------------
> Damon McDougall
> Mathematics Institute
> University of Warwick
> Coventry
> CV4 7AL
> d.m...@wa...
>
> On 22 Nov 2009, at 21:34, Xavier Gnata wrote:
>
>    
>> Hi,
>>
>> RTFM...indeed it works.
>> However, the axis do not scale accordingly:
>>
>> quiver([1],[1],[2],[2], angles='xy', scale_units='xy', scale=1) on a TkAgg backend produce a plot with:
>> In [11]: axis()
>> Out[11]:
>> (0.94000000000000006,
>> 1.0600000000000001,
>> 0.94000000000000006,
>> 1.0600000000000001)
>>
>> The display area scales the same way as it does using quiver([1],[1],[2],[2]) (without any other args).
>> It looks like a bug.
>>
>> Xavier
>>
>>
>>      
>>> Hi Xavier,
>>>
>>> You can pass some handy keyword arguments to fix that. Use the following:
>>>
>>> quiver([1],[1],[1.2],[1.2], angles='xy', scale_units='xy', scale=1)
>>>
>>> Hope that helps :)
>>>
>>>
>>> Regards,
>>> -- Damon
>>>
>>> --------------------------
>>> Damon McDougall
>>> Mathematics Institute
>>> University of Warwick
>>> Coventry
>>> CV4 7AL
>>> d.m...@wa...
>>>
>>> On 22 Nov 2009, at 16:37, Xavier Gnata wrote:
>>>
>>>
>>>        
>>>> Hi,
>>>>
>>>> I woud like to draw a vector field using pylab.
>>>> quivert looks nice but it sould not scale the arrows to fit my use-case.
>>>> quiver([1],[1],[1.2],[1.2]) does plot a nice arrow but the head of the
>>>> arrow is not at (1.2,1.2).
>>>> Is there a way to plot a list of arrows *without* any scaling?
>>>>
>>>> Xavier
>>>>
>>>> ------------------------------------------------------------------------------
>>>> Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day
>>>> trial. Simplify your report design, integration and deployment - and focus on
>>>> what you do best, core application coding. Discover what's new with
>>>> Crystal Reports now.  http://p.sf.net/sfu/bobj-july
>>>> _______________________________________________
>>>> Matplotlib-users mailing list
>>>> Mat...@li...
>>>> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>>>>
>>>>          
>>>
>>>        
>>      
>    

Hi Xavier,

I'm sorry. As I don't know a great deal about the nuts and bolts of matplotlib, I don't think I'm well enough equipped to answer your question. Perhaps someone else on this list can help out?


Regards,
-- Damon

--------------------------
Damon McDougall
Mathematics Institute
University of Warwick
Coventry
CV4 7AL
d.m...@wa...

On 23 Nov 2009, at 21:00, Xavier Gnata wrote:

> Hi,
> 
> Well when you plot, imshow or whatever is matplotlib related, the axes do scale *automatically*.
> Why should it be different with quiver?
> 
> I do reproduce your error with axis('tight')
> 
> 
> Xavier
> 
>> Hi Xavier (cc list),
>> 
>> It may be a bug, however I do not know what the default behaviour 'should' be. You could do:
>> 
>> lims = [-4, 4, -4, 4]
>> axis(lims)
>> 
>> after calling quiver to see the whole arrow. I did notice that calling
>> 
>> axis('tight')
>> 
>> threw the following error
>> 
>> /Users/Damon/python/lib/matplotlib/axes.py:2038: UserWarning: Attempting to set identical xmin==xmax results in singular transformations; automatically expanding.  xmin=1.0, xmax=1.0
>>   warnings.warn('Attempting to set identical xmin==xmax results in singular transformations; automatically expanding.  xmin=%s, xmax=%s'%(xmin, xmax))
>> /Users/Damon/python/lib/matplotlib/axes.py:2212: UserWarning: Attempting to set identical ymin==ymax results in singular transformations; automatically expanding.  ymin=1.0, ymax=1.0
>>   warnings.warn('Attempting to set identical ymin==ymax results in singular transformations; automatically expanding.  ymin=%s, ymax=%s'%(ymin, ymax))
>> 
>> is this correct, or is it a bug? I'm using "ipython -pylab" with the MacOSX backend. I was expecting axis('tight') would scale the axes so I could see the whole arrow.
>> 
>> 
>> Regards,
>> -- Damon
>> 
>> --------------------------
>> Damon McDougall
>> Mathematics Institute
>> University of Warwick
>> Coventry
>> CV4 7AL
>> d.m...@wa...
>> 
>> On 22 Nov 2009, at 21:34, Xavier Gnata wrote:
>> 
>>   
>>> Hi,
>>> 
>>> RTFM...indeed it works.
>>> However, the axis do not scale accordingly:
>>> 
>>> quiver([1],[1],[2],[2], angles='xy', scale_units='xy', scale=1) on a TkAgg backend produce a plot with:
>>> In [11]: axis()
>>> Out[11]:
>>> (0.94000000000000006,
>>> 1.0600000000000001,
>>> 0.94000000000000006,
>>> 1.0600000000000001)
>>> 
>>> The display area scales the same way as it does using quiver([1],[1],[2],[2]) (without any other args).
>>> It looks like a bug.
>>> 
>>> Xavier
>>> 
>>> 
>>>     
>>>> Hi Xavier,
>>>> 
>>>> You can pass some handy keyword arguments to fix that. Use the following:
>>>> 
>>>> quiver([1],[1],[1.2],[1.2], angles='xy', scale_units='xy', scale=1)
>>>> 
>>>> Hope that helps :)
>>>> 
>>>> 
>>>> Regards,
>>>> -- Damon
>>>> 
>>>> --------------------------
>>>> Damon McDougall
>>>> Mathematics Institute
>>>> University of Warwick
>>>> Coventry
>>>> CV4 7AL
>>>> d.m...@wa...
>>>> 
>>>> On 22 Nov 2009, at 16:37, Xavier Gnata wrote:
>>>> 
>>>> 
>>>>       
>>>>> Hi,
>>>>> 
>>>>> I woud like to draw a vector field using pylab.
>>>>> quivert looks nice but it sould not scale the arrows to fit my use-case.
>>>>> quiver([1],[1],[1.2],[1.2]) does plot a nice arrow but the head of the
>>>>> arrow is not at (1.2,1.2).
>>>>> Is there a way to plot a list of arrows *without* any scaling?
>>>>> 
>>>>> Xavier
>>>>> 
>>>>> ------------------------------------------------------------------------------
>>>>> Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day
>>>>> trial. Simplify your report design, integration and deployment - and focus on
>>>>> what you do best, core application coding. Discover what's new with
>>>>> Crystal Reports now.  http://p.sf.net/sfu/bobj-july
>>>>> _______________________________________________
>>>>> Matplotlib-users mailing list
>>>>> Mat...@li...
>>>>> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>>>>> 
>>>>>         
>>>> 
>>>>       
>>>     
>>   
>