Re: Matrix like operations in a .oct file

[babelproofreader]

Kai Torben Ohlhus-2 wrote
> On Fri, Oct 4, 2013 at 12:03 AM, babelproofreader <

> babelproofreader@

>> wrote:
> 
>> 
> <snip>
>>
>> the revelant part of my code is:-
>>
>>  Matrix price = args(0).matrix_value () ; // a single column matrix
>>  Matrix output = args(0).matrix_value () ;
>>
>>  // create intermediate calculation matrices
>>  Matrix vec_11 (1,11) ;
>>  Matrix price_11 (11,1) ;
>>  Matrix result (1,1) ;
>>
>>  for ( int ii = -m ; ii < (m+1) ; ii ++ )
>>      {
>>      vec_11 is filled in this loop and then doesn't change
>>      }
>>
>>  for ( octave_idx_type ii (50) ; ii < args(0).length () ; ii++ )
>>      {
>>      // extract rolling window and perform matrix multiplication
>>      result = vec_11 * price.extract(ii-10,0,ii,0) ;
>>      output(ii,1) = result ; // this writing to output matrix fails
>>      }
>>
>>  retval_list(0) = output ;
>>
>> 
> <snip>
>>
> 
> Hello,
> 
> Your code structure looks to me, that you want to perform the matrix
> manipulation in-place. You refer with price and output to the same input
> matrix. This is a problem. You are writing a function, that returns a
> matrix. For your case these two calls will be possible:
> 
> A = yourFunction (A);
> B = yourFunction (A);
> 
> For the first case, there is no problem. But the second case gets weird. A
> and B refer to the same storage When you proceed in the command line, you
> wouldn't necessarily expect, that changes on B affect Matrix A as well. To
> avoid this better create a new output matrix in your *.oct-File (see:
> http://octave.sourceforge.net/doxygen/html/d3/d3f/classMatrix.html)
> 
> Matrix output (price.rows (), price.cols());
> 
> If you need further help, could you please provide a more complete
> example?
> It is hard to guess where the problem is by this small excerpt.
> 
> Best,
> Kai
> 
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Matrix output (price.rows (), price.cols()); this doesn't change things. The
problem boils down to writing "result" to "output," i.e. output(ii,1) =
result ; // this writing to output matrix fails



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