Added some iterating methods to Matrix (issue #57)

[SamoylovMD]

Added: each, eachInRow, eachInColumn methods;
Renamed each method to eachNonZero.

[vkostyukov]

Test are failed, since there is a usage if each in MatrixMarketStream. So, we need to change it to new eachNonZero call.

[vkostyukov]

This is not a good idea. The getRow is extreamally slow method. We need to iterate in straightforward way. Like:

for (int j = 0; j < columns; j++) {
  procedure.apply(i, j, get(i, j));
}

[vkostyukov]

Hi Maxim @SamoylovMD,

Please also add eachNonZeroInRow() and eachNonZeroInColumn() implementations. And we can provide more efficient implementation of eachNonZeroInRow() for CRS matrix and eachNonZeroInColumn for CCS matrix. For other cases, it would be enough to have general implenetation in AbstractMatrix class.

Please, also follow my coments to improve the code.

[vkostyukov]

Why do we need this?

[vkostyukov]

I don't think this is correct. We need a separate implementation for non-zero elements here.

[SamoylovMD]

Ofc, my error. Will rewrite in few seconds.

[SamoylovMD]

Fixed in new commit.

[vkostyukov]

I would prefere to have spaces here. Like

procedure.apply(i, j, get(i, j));