The differential operator $ D_{+}D_{-} $ discretizes the
second derivative with the second-order formula
$$ \frac{\partial^2 u_{i}}{\partial x^2} \approx
\frac{u_{i+1}-2u_{i}+u_{i-1}}{h^2} = D_{+}D_{-} u_{i}
$$
test the correctness of the returned values is tested by
checking them against numerical calculations.
solve linear system for a given right-hand side
without result Array allocation. The rhs and result parameters
can be the same Array, in which case rhs will be changed
$ D_{+}D_{-} $ matricial representation
The differential operator $ D_{+}D_{-} $ discretizes the second derivative with the second-order formula $$ \frac{\partial^2 u_{i}}{\partial x^2} \approx \frac{u_{i+1}-2u_{i}+u_{i-1}}{h^2} = D_{+}D_{-} u_{i} $$
test the correctness of the returned values is tested by checking them against numerical calculations.