Run testrtrl and type a number between 1 and 6 to select a demo.  The
top plot is the error per sample.  The rest of the plots
show the inputs, targets, and outputs.  

Consider the first choice,  1. 2-bit xor, delay is 2, 1 cycles.  For
this task, the recurrent net is given two binary-valued inputs,
contains four units, and the output of the fourth unit is trained to
produce the xor of the two inputs that occurred two steps in the past.
1 cycle means that the error is backpropagated every step.  So, the
plots show, in order from top to bottom,

- RMS error per sample
- input 1  (x1)
- input 2  (x2)
- target (x1 xor x2 for values of x1, x2 at time t-2)
- output of unit 4 (the trained one that should duplicate the target)
- output of unit 3
- output of unit 2
- output of unit 1

Now consider choice 2,  2. 1-bit identity, 4 step delay, 1 cycle, random input
This task has one binary-valued input, and four units including one
trained unit.  The target is the input four steps ago, so this is just
learning a four-step delay.  This example doesn't always converge
before training quits.

Choice 3, bit 1 followed indefinitely by bit 2, 1 cycle, random input,
is a task with two binary-valued inputs, two units including one
trained to produce a high output when the second input becomes nonzero
the first time after the occurrence of a nonzero first input.  The net
must learn to remember that bit 1 has occurred until bit 2 appears.
When bit 2 appears, the memory of bit 1 is erased.

The last three choices are not working demos.  I decided to include
them here for others as a possible starting point for using this code
to learn models of dynamic systems.

Choice 4,  second order system, given state variables as input, is a
task with two real-valued inputs that are the two state variables of a
simple linear system.  The net has two units with one trained to
duplicate the first state variable.

Choice 5 is the same linear system, but now the input is just a
history of one of the state variables.

Choice 6 is for a third order system, a suspension system. The net is
given one state variable and action as input.