This can be switched off via --disable-assumed-size

Sometimes it might be desirable that only one of the specifc AVX
kernels (AVX, AVX2, and in the future AVX512) are build, even though the processor
supports all (or several) of these instructions.

The flag --disable-[avx | avx2 | avx512] allows to define which kernels
should NOT be build. The default is: what can be build will be build

A random matrix is set up, and then result = a**T * 2*b is computed
this is compared with the result of plain scalapack routines and
the maximum norm of "scalapack - elpa" is computed (should be zero on
machine precision)