Name of function is cleared after val_graph optimization

[metab0t]

The name of function is reset after val2fun but is unchanged if we do not use val_graph optimization. Should the behavior be consistent across different optimization options?

CppAD/include/cppad/local/val_graph/val2fun.hpp

Line 1000 in 7a81cb7

function_name_ = "";

[bradbell]

The val2fun optimization is experimental. It is much easier to understand, but it take a lot of time to convert from and to a val_graph representation.

I plan to make an optimizer that is simpler, like val_graph, but not slower.