problem with an integral

A system obey an equation of motion y''=f(y'(t),y(t),t) but f(y'(t),y(t),t) change as a function of y(t).

For example if y>=0 then y''=g(y'(t),y(t),t) and if y<0 then y''=h(y'(t),y(t),t).

Is it possible to write a script with a solver that can integrate "the right function at the right moment"? Anyone could help me? Thanks a lot!

Answer 1

[Walter Roberson]

y'' = Heaviside(y) * g(y'(t),y(t),t) + Heaviside(-y) * h(y'(t),y(t),t)

Provided, that is, that Heaviside(x) is defined as 0 when x is 0.