Merge branch '40-multirhstest-fails-to-compile-when-arpack-is-installed' into 'master'

Resolve "multirhstest fails to compile when arpack++ is installed"

Closes #40 (closed)

See merge request !161 (merged)

(cherry picked from commit 9d012149)

3fcec40b Fix condition estimate for exotic number types 76b9f4e9 Fix condition estimate for exotic number types, clang edition

This should fix the pipelines on the 2.6 branch (e.g. https://gitlab.dune-project.org/core/dune-istl/pipelines/6505) that have been failing since infrastructure/issues0#48 (closed) was adressed.

merged

mentioned in commit 222809e0

mentioned in merge request !167 (merged)