question using evolution2d with an ODE



Hi I'm brand new to maxima, and I hope it is okay to ask questions on this
mailing list.

I'd like to use evolution2d

( see http://maxima.sourceforge.net/docs/manual/en/maxima_50.html)

to look at iterations for a flow with a certain time step.

or  phi_t(phi_t(xo)) = phi_2t(xo)  etc

What I tried was  integrating the ODE to the required time where x is my
initial condition then picking out the last value.  (Notice the apostrophe
in front of last and rk)

define(f(x),'last('rk(exp(-t) + u, u,x,[t,2,7,0.01]))[2]);

If I type    say  f(-0.1),nouns  I do get the answer I'm looking for but
I've been unable to put this line into a functions.   For instance I tried

g(x) := nouns(f(x))  and   define(g(x), (f(x),nouns)) but no success.

I'd appreciate any help and also if someone can think of a better way to
approach this problem I'd appreciate it.

Thank you,

Steve