[CppAD] yq = f.Forward(q, xq): a zero order Taylor coefficient is nan. What usually causes it?

[Brad Bell]

If the zero order Taylor coefficient is nan, the function value is nan. So you should be able to 
evaluate the original function using the xq values. There are facilities for determining the x value 
at which the nan occurs if you do not know that; see the heading Error Message on
https://coin-or.github.io/CppAD/doc/check_for_nan.htm#Error%20Message



On 4/20/20 4:53 PM, Hank xu wrote:
> Hi,
>
> I'm a new user of CppAD library and am trying to use it with Ipopt. I implemented my formulation 
> following the format from this example 
> <https://www.coin-or.org/CppAD/Doc/ipopt_solve_get_started.cpp.htm>, and now is stuck with this error;
>
>  yq = f.Forward(q, xq): a zero order Taylor coefficient is nan
>
> After both searching online and looking through source code, I could not figure out the root 
> cause of this error. I'm not too familiar with the automatic differentiation field and would love 
> to get some help on how to tackle this. Any help would be greatly appreciated!
>
> Best,
> Haoyun
>
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