contourc - Octave vs Matlab

[Kai Habel]

Ben Abbott schrieb:
> On Apr 4, 2009, at 1:03 PM, Big Muscle wrote:
>
>   
>> Hello.
>>
>> Is Octave’s contourc algorithm supposed to produced exactly same  
>> contours as Matlab algorithm? I would like to use Octave’s source  
>> code to my application, but it doesn’t provide same result as  
>> Matlab. The difference is that Matlab draws some countours at same  
>> level as two different contours, but Octave draws it as one.
>>
>> I also tried to use PLPlot algorithm, but it has completely inversed  
>> problem – it sometimes draws two closed contours where Matlab draws  
>> only one closed contour.
>>
>> I think my problem has something to do with saddle points where both  
>> algorithms use different techniques to choose which edges to connect.
>> Is there something to do with this? Thank you!
>>
>> Tomas
>>     
>
> I'm confused as to the specifics. Can you provide a simple example  
> illustrating the difference between Octave and Matlab?
>
> Ben
>
>
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>   
Try the following in octave and matlab:

A=zeros(4);
A(2,2)=1;
A(3,3)=1;
subplot(1,2,1);
contour(A,[0.5,0.5]);
B=zeros(4);
B(2,3)=1;
B(3,2)=1;
subplot(1,2,2);
contour(B,[0.5,0.5]);

octave creates for A a single contour, while matlab creates two. For B 
both create two contours. All results are valid, but it seems matlab is 
more consistent. If my time allows I will have a look at __contourc__.cc 
and see if there is an easy fix ... but no promises.

Kai