We recently encountered a rather strange issue when passing denormal numbers in the right-hand-side matrix to ZGETRS. Attached is a small C++ file that reproduces this error.
In this file, we set up a left- and right-hand-side matrix, factorize the lhs with ZGETRF and then call ZGETRS. Before and after the call to ZGETRS, we call the standard math fmod function with some arbitrary numbers. The call to fmod that happens before the ZGETRS call works as expected. The call afterwards however returns nan, regardless of what numbers are passed.