Sorry for this late answer but we had to discuss this issue internaly and make some tests. You can use either 'general' or 'advanced refinement' option to define your polynomial root accuracy. However there is no detailed documentation about this.
In our experience, 'general' option is fast, normally with 6-10 digits accuracy, depending on polynomial order and type (like repeated
roots). But one disadvantage is 'general' option can not ensure the
roots are exactly real or complex conjugated.
'advanced refinement' can ensure the roots are either real or complex
conjugated, normally with higher digits accuracy than 'general'
option. It can deal with repeated roots situation. But it is slower
than 'general' option.
For other two options, you
should have some knowledge about the polynomial.
I hope that helps.
Yannick.
