function yprime = bump_ode ( x, y )
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%  function yprime = bump_ode ( x, y )
%
%  computes the derivative for the bump ODE:
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%    Y' = -Y^2
%
%  whose solution, given y(0) = 1, is y(x) = 1 / ( 1 + x ).
%
yprime = - y * y;