nd-order runge-kutta method algorithm allocate argument keyword named ordinary positional array element index slice of sorting asarray (function) assert (function) assignment atan axis (plot) boolean expression false true boundary conditions brute force method bug ++ calculator cell class closure code exception re-use robust try-except colon comment commenting code compartment model composite midpoint method composite trapezoidal rule computational speed (measuring) computer program convergence rate copy crank-nicolson method debugger debugging def default demo function difference absolute backward centered forward relative differential equation first-order second-order diffusion equation discontinuous coefficient divergence doc string doconceix domain complex double integral midpoint double sum dynamical system