TODO carefully investigate QUDA mixed solver parameters

[kostrzewa]

Investigate the interaction of

• rel_delta / use_alternative_reliable
• max_res_increase
• max_res_increase_total

On the one hand, this is relevant for multi-shift CG with mixed-precision refinement for the 1+1 sector, on the other hand, it is also relevant for intermediate and large tm_rho shifts in the determinant and determinant ratios.

[kostrzewa]

Initial investigation

compare_mixed_cg.pdf

suggests that rel_delta = 1e-1 should be set for sloppy == half and for safety, the defaults for max_res_increase and max_res_increase_total should be relaxed.