It seems this initialization is syntactically not correct.
clang says:
`TestCoordinatesMapping.cpp:451:18: error: variable-sized object may not be initialized
    double exp_J[this->dim*this->dim]= {0.0};
`
Even if the array's size would be a constant, the `{0.0}` would initialize only the first element.
I don't know better solution than `std::fill_n(exp_J, dim*dim, 0);`