1D Helmholtz problem (\(Q=0\)). Exact and FIC–FEM results for a uniform mesh of eight 2-noded elements of length \(l^e\). a\(\gamma =0\), \(\omega =-5\); b\(\gamma =0\), \(\omega =-100\)\(\left( \gamma = \frac{\rho c u l^e}{2k}, w = \frac{s(l^e)^2}{k}\right) \) [6, 28]