In numerical analysis, when approximating functions using polynomial interpolation with equally spaced interpolation points, it may be the case for some functions that using more points creates worse approximations, so that the interpolation diverges from the function it is trying to approximate rather than converging to it. This paradoxical behavior is called Runge's phenomenon. It was first discovered by Carl David Tolmé Runge for Runge's function formula_16, another scaled version of the witch of Agnesi, when interpolating this function over the interval formula_17. The same phenomenon occurs for the witch formula_18 itself over the wider interval formula_19.