Improved Random butterfly transform

[asenzz]

Hi guys, as previously discussed with Abdelfattah I uploaded an improved magma_*gesv_rbt_async version of Magma to https://bitbucket.org/zarkoasen/magma-tempus/src/gesv_rbt_async_2.9.x/

This implementation has slightly improved execution time and higher precision for complex problems because it saves the best solution over many iterations of refinement and can also have the number of iterations and threshold set in the call arguments.

Please let me know if you decide to integrate any of my changes in the mainstream code.

[mgates3]

@asenzz Can you open a pull request to MAGMA with your changes?

[asenzz]

my fork is on Gitlab and MAGMA moved in the mean time to Github, you can see my implementation of zgesv_rbt_async and zgesv_rbt_refine at https://bitbucket.org/zarkoasen/magma-tempus/src/gesv_rbt_async_2.9.x/src/zgesv_rbt.cpp#lines-206 and start porting from there. Note that it includes and uses other functions that end with _async these are new functions I introduced that require a magma_queue_t parameter and need to be included when porting. Some of them may be obsolete by now but I still think its worth including this code I got a slight improvement in accuracy and about 30% improvement in speed when used in kernel parameters tuning for support vector regression.

[mgates3]

The MAGMA team accepts contributions as pull requests. We are a small team and don't have the personnel to manually port code into MAGMA.

[asenzz]

I'll try and make another fork on Github when I find the time.

[asenzz]

The pull request is here please review and a unit test needs to be written #62