What would be the best way to convert the following to a generic ArrayBase type?

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inline Eigen::ArrayXd db10(Eigen::ArrayXd x) { return 10.0/log(10.0) * x.abs().log(); };
inline Eigen::ArrayXd db10(Eigen::ArrayXcd x) { return 10.0/log(10.0) * x.abs().log(); };


I think I can figure out the first case (both argument and return are double), but the second case (argument is complex, return is double) is not clear to me.

Thanks.

you can use typename Derived::RealScalar for the scalar type of the returned Array object.

Associated with this (maybe if I fix this one, I can fix my original issue), I have working code for an inplace function:

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  template <typename Derived>
  void my_swap_inplace(const Eigen::DenseBase<Derived>& x_)
  {
    Eigen::DenseBase<Derived>& x = const_cast< Eigen::DenseBase<Derived>& >(x_);
    x.block(0,0,x.rows()/2,x.cols()).swap(x.block(x.rows()/2,0,x.rows()/2,x.cols()));
  }

And I want a non-inplace version (one returning a value). I've tried various code fragments like:

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  template <typename Derived, typename OtherDerived>
  typename Eigen::DenseBase<Derived>::PlainObject my_swap(const Eigen::DenseBase<OtherDerived>& x)
  {
    typename Eigen::DenseBase<Derived>::PlainObject y = x.derived();   
    y.block(0,0,y.rows()/2,y.cols()).swap(y.block(y.rows()/2,0,y.rows()/2,y.cols()));
    return y;
  }

But have not been successful in getting to compile. Any ideas? Thanks.

remove the OtherDerived template parameter, and use Derived everywhere.

Thanks. That's what I tried first:

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  template <typename Derived>
  typename Eigen::DenseBase<Derived>::PlainObject my_swap(const Eigen::DenseBase<Derived>& x)
  {
    typename Eigen::DenseBase<Derived>::PlainObject y = x.derived();   
    y.block(0,0,y.rows()/2,y.cols()).swap(y.block(y.rows()/2,0,y.rows()/2,y.cols()));
    return y;
  }

But get a "No matching function" error on compile.

How do you call it? Perhaps you could also directly use the input type:

template <typename T>
typename T::PlainObject my_swap(const T& x)
{
typename T::PlainObject y = x.derived();
...

Thanks. Directly using the input type worked fine.

For the initial problem of returning a real scalar I ended up with:

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template <typename Derived>
typename Eigen::Array<typename Derived::RealScalar, Derived::RowsAtCompileTime, Derived::ColsAtCompileTime>::PlainObject
db10(const Eigen::ArrayBase<Derived>& x)
{ 
  return 10.0/log(10.0) * x.derived().abs().log();
}

which seems to work fine for all array types. Please let me know if there was a better way (other than the ReturnByValue class I've seen described at http://listengine.tuxfamily.org/lists.t ... 00216.html which is probably overkill for this case). Thanks.