[scientific computation] In solving partial differential
equations by finite difference and similar methods, wiggles
are sawtooth (up-down-up-down) oscillations at the shortest
wavelength representable on the grid. If an algorithm is
unstable, this is often the most unstable waveform, so it
grows to dominate the solution. Alternatively, stable (though
inaccurate) wiggles can be generated near a discontinuity by a
Gibbs phenomenon.