Re: [eigen] Feature suggestion: interior row and column ranges [patch attached]

[Gael Guennebaud <gael.guennebaud@xxxxxxxxx>]

hi,

thanks for the patch.

Let's discuss function names: to be consistent with
bottomRows/topRows/leftCols/rightCols, they should be: rows(int,int)
and cols(int,int), but then there is a name clash with rows() and
cols() returning the matrix sizes.  In the sparse module I used
subRows, and subCols for the same feature because I wanted names that
finish by "rows" and "cols", but they are not very good names! So yes
why not colRange and rowRange. I'm not 100% convinced, but since I
have nothing better to propose...

gael

On Sat, Jun 26, 2010 at 11:52 PM, Manoj Rajagopalan <rmanoj@xxxxxxxxx> wrote:
>
>
>
> On Saturday 26 June 2010 05:32:31 pm FMDSPAM wrote:
>>   Am 26.06.2010 22:58, schrieb Manoj Rajagopalan:
>> > Hi,
>> >
>> >    I've noticed leftCols(), rightCols(), topRows() and bottomRows() in
>> > the DenseBase API. I have, on occasion felt the need to access a
>> > contiguous range of rows/columns that start and end in the interior - the
>> > above functions allow access only to the extremes. Could DenseBase member
>> > functions, possibly named colRange(Index start, Index size) and
>> > rowRange(Index start, Index size), be supported sometime in the future?
>> >
>> > Thanks,
>> > Manoj
>>
>> It's already in upcomming eigen 3.0:
>> Use dynamic sized block: mat1.block(i,j,rows,cols)
>> or fixed sized block: mat1.block<rows,cols>(i,j)
>> to have Read-write access to sub-matrices.
>>
>> see devel-doc:Tutorial Matrix Blocks
>> <http://eigen.tuxfamily.org/dox-devel/TutorialCore.html#TutorialCoreMatrixB
>>locks>
>>
>> cheers
>> Frank
>
>
>
> Attaching a patch implementing my suggestion for the consideration of the
> developers/maintainers.
>
> @Frank: I wished the API would let me choose, say 3 columns starting with the
> 4th, in a 10x10 matrix. This should be a 10x3 submatrix starting at column #3
> (0-base-indexing). With leftCols() (or rightCols()), the starting (or ending)
> column is fixed to an extreme and there is currently no API method to extract
> a few contiguous columns or rows purely in the interior.
>
> DenseBase::block() is the master method that allows the access of any
> contiguous 2D sub-region and is used to implement leftCol() and rightCol()
> but the latter are much more readable functions. So I present
> DenseBase::rowRange() and DenseBase::colRange() which use DenseBase::block()
> to extract contiguous interior rows and columns respectively.
>
> Example of rowRange usage:
>
>        int const N = 10;
>        MatrixXi A(N,N);
>        A.setRandom();
>        cout << "A =\n" << A << '\n' << endl;
>        cout << "A(3..5,:) =\n" << A.rowRange(3,3) << endl;
>        // alternatively, since #cols is known at compile time
>        cout << "A(3..5,:) =\n" << A.rowRange<3>(3) << endl;
>
> Output:
>
> A =
>  7   0 -10   0   1   1  -5   1   4  10
>  -2   3  -5   7   6  -9  10 -10  -7   2
>  6  -3  -8   2  -2  -6   8  -1  -1   3
>  6   0   6  -4   8   3   7   9   8   8
>  9   9  -7   3  -5   8  -5   9   7  -1
>  -6   9  -2   1  -3  -3   1   5  -4   9
>  -3   3  -8   0   6  -9  -3  -5  -6  -2
>  6   5  -8  10   9 -10   5   5   8   7
>  -5  -8  10  -4  -9  -1   0   3  -3   4
>  1   2  -6   6   9  -9   4  -3   4   9
>
> A(3..5,:) =
>  0   1   1
>  7   6  -9
>  2  -2  -6
>  -4   8   3
>  3  -5   8
>  1  -3  -3
>  0   6  -9
>  10   9 -10
>  -4  -9  -1
>  6   9  -9
>
>
> I have written small test programs like the above and have tested static and
> dynamic versions of rowRange() and colRange().
>
> Thanks,
> Manoj
>