Environment: IFS 36r4. This bug was observed using the following compilers and MPI libraries:

• Intel 2017.4 & Intel MPI 2017.4

The problem was reported when using -O2 & -O3 optimization flags in conjunction with activation of AVX-512, aka 512-bit SIMD or which is the same, 512-bit vector extensions.

Problem: Running IFS with O3 (the highest optimization level) and activating AVX-512 makes the model exit due to a singular matrix (a matrix that does not have an inverse) that cannot be used to solve the system of equations in the physics part.

Actions taken:

Diagnosis:

Solution:

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