Re: Techniques in using liboctave and liboctinterp from C++ program

[Jaroslav Hajek]

On Fri, Jun 27, 2008 at 3:01 PM, John Swensen <address@hidden> wrote:
>
> On Jun 26, 2008, at 1:56 PM, dbateman wrote:
>
>>
>>
>>
>> John Swensen wrote:
>>>
>>> I have started using the datatypes and operations of Octave from C++
>>> for my research and have a few questions.
>>>
>>> 1) Can builtin functions and DLD-FUNCTIONS (e.g. find, eig, conv2,
>>> etc) be used directly from C++?
>>>
>>
>> You can always use feval to call an m-file or oct-file. You can't
>> really
>> call an oct-file directly from C++. What you can have for example is
>> if the
>> oct-file calls another C++ function, you might declare that function
>> extern
>> and call it as well, though the oct-file would have to be loaded first
>>
>>
>>
>>> 2) In the documentation, is there a list of overloaded operators for
>>> octave_value objects of different types?  For example, I was trying
>>> to
>>> do the following:
>>> Matrix A(768,1024);
>>> Matrix B(1,1);
>>> Matric C = A*B;
>>> This, however, didn't work.  Instead, I had to declare B as a scalar
>>> double as follows:
>>> Matrix A(768,1024);
>>> double b;
>>> Matrix C = A*B;
>>> This isn't necessarily a problem, but it would be nice if there was a
>>> list of possible overloads somewhere.
>>>
>>
>> That's not so easy for two reasons. Firstly someone has to do the
>> work of
>> documenting them. However, the second reason is harder. Having
>> documented
>> these functions they then define an API to the internals of Octave,
>> something that has never really been stable. Therefore some thought
>> needs to
>> go into this process of what functionality to document in an API.
>>
>>
>>
>>> 3) I often do image thresholding after I have processed it a bit.  In
>>> the Octave interpreter I can simply type 'im2 = im1>0.5'.  I tried
>>> doing the following, but it didn't work:
>>> Matrix A(768,1024);
>>> double B = 0.5;
>>> Matrix C = A>B;
>>> If I could find out where that bit of the interpreter was
>>> implemented,
>>> I could figure it out, but I searched through the sources a bit and
>>> couldn't find anything.
>>>
>>
>> I don't have a copy of Octave with me, but check the file
>> src/OPERATORS/op-m-m.cc for the gt function and see what it does.
>>
>> D.
>> --
>> View this message in context: 
>> http://www.nabble.com/Techniques-in-using-liboctave-and-liboctinterp-from-C%2B%2B-program-tp18137086p18139690.html
>> Sent from the Octave - General mailing list archive at Nabble.com.
>>
>> _______________________________________________
>> Help-octave mailing list
>> address@hidden
>> https://www.cae.wisc.edu/mailman/listinfo/help-octave
> So I have kindof muddled my way through the operator business.  Once I
> got my head wrapped around all the #define's, it makes a lot of
> sense.  However, the comparator operators are still not working.  I
> can get it to compile fine, but every time I try to do a compare, I
> get a "fatal: T& Array<T>::checkelem (10, -1, -1): range error" error
> message.
>
> Here is a very simple example that causes the problem:
> // compile with 'mkoctfile --link-stand-alone test.cpp -o test'
> #include "octave/config.h"
> #include "octave.h"
> #include <octave/ov.h>
>
> // Standard C++ includes
> #include <iostream>
> #include <string>
> #include <vector>
> #include <map>
> using namespace std;
>
> int main (int argc, char* argv[])
> {
>   octave_value tmp1(0.5);
>   octave_value tmp2(1.0);
>   octave_value tmp3(0.5);
>
>   tmp1 == tmp2;
>
>   return 0;
> }
>
> I'm assuming this is some sort of indexing error, since the
> checkelem() function in Array.h appears to be checking indices.  What
> I don't understand is why it thinks these two scalar octave_values are
> somehow 3-dimensional.  Why isn't it using the checkelem() that
> appears to be tailored for single dimensional octave_values?
>
I believe it is not, you just see a random error. I get a segfault
with the same program.
The problem is that you invoke binary ops on octave_value objects, but
the typeinfo instance is not initialized. You can do this manually by
calling the instance_ok static method. Your program still won't work
as the types and ops must be registered first, but at least it will
give you a proper error message. See install_types() and install_ops()
for registering all common types and ops. I believe this also
eliminates the need to initialize typeinfo manually.


cheers


> John Swensen
> _______________________________________________
> Help-octave mailing list
> address@hidden
> https://www.cae.wisc.edu/mailman/listinfo/help-octave
>



-- 
RNDr. Jaroslav Hajek
computing expert
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz