function f = jagged(x,n,a,s)
%JAGGED Computes an approximation of a continuous nowhere
% differentiable function.
% (By Douglas Arnold who happens to be at Penn. State U.)
%
% jagged(x,n,a,s) is __
% \ | n (s-2)m m
% > a sin(a x).
% /__| m=0
% In the limit as n->infinity this gives a continuous nowhere
% differentiable function if a>1 and 1