Re: [eigen] Using custom scalar types.

[Brad Bell <bradbell@xxxxxxxxxx>]

I was able to fix this problem by defining a partial specialization for
    template<typename Scalar, bool IsInteger>
    struct significant_decimals_default_impl
which is defined in Eigen/src/Core/IO.h. The partial specialization can 
be in the change set
    https://projects.coin-or.org/CppAD/changeset/2792#file10

Perhaps there is some other way (without defining a cast from AD<Base> 
to int) that the same thing can be accomplished and that is documented 
and hence part of the Eigen API ?



On 04/22/2013 07:15 PM, Brad Bell wrote:
> If I compile the program:
> ====================
> # include <cppad/cppad.hpp>
> # include <cppad/example/cppad_eigen.hpp>
>
> int main()
> {
> typedef Eigen::Matrix< CppAD::AD<double>, 1, 1> MatrixAD;
> MatrixAD X;
> X(0, 0) = 1;
>
> std::cout << X << std::endl;
> return 0;
> }
> ====================
> using eigen-3.1.3 with the trunk for the package
> http://www.coin-or.org/CppAD/
> I get the error message
> .../include/Eigen/src/Core/IO.h:132:97: error: no matching function 
> for call to ‘ceil(CppAD::AD<double>)’
> Looking at the corresponding code I see the code
> return 
> cast<RealScalar,int>(ceil(-log(NumTraits<RealScalar>::epsilon())/log(RealScalar(10))));
>
> On the page
> http://eigen.tuxfamily.org/dox-devel/TopicCustomizingEigen.html
> under the heading
> Using custom scalar types
> I see mention of
> "define the math functions that makes sense for your type."
> and perhaps ceil could be considered one such function. But I do not 
> see mention of conversion from the scalar type to int, which also 
> seems to be required ?
>
> The problem is that, for AD types, I think that implicit conversion to 
> int is dangerous because the AD information is lost and hence CppAD 
> provides an explicit function for this purpose
> http://www.coin-or.org/CppAD/Doc/integer.xml
>
> Perhaps it would be OK if one restricts the casting operator to be 
> explicit, but as I understand this is a c++11 extension and not 
> available in c++98.