[CppAD] Automatic differentiation of tanh fails for some values

[Srikrishnan Ramadurai]

Hi,

I am trying to find the jacobian for a function that has a few tanh
functions in it . I've noticed that the differentiation of tanh function
fails for some arguments.

A test example  is y=tanh(c*x1)+x2

The Jacobian of y is obtained when c is small say 20, but fails with an
error when c is something like 100. This is using the driver function
Jacobian.

This is the error that I receive.

cppad-20110711 error from a known source:
y_p = f.Forward(p, x_p): has a nan in y_p for p = 0.
Error detected by false result for
    false

Is there something that I need to do to make the differentiation work? Any
help is appreciated.

The sample code in c++ is attached. The system is a intel core 2 quad
machine running on 64 bit ubuntu 10.04.

Thanks.

Regards
Srikrishnan
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