Which solver to use for IE

IE is a moment of method techniques used in SBR+ and Hybrid. It can use MLFMM or ACA, which one is better

It is highly recommended to choose Auto. MLFMM Multi-Level Fast Multipole Method is faster and uses less space. ACA Adaptive Cross Approximation is better if you have less than 100000 unknowns. Also for highly skewed aspect ratio (triangular elements ratio), ACA is better.