Re: [eigen] DenseBase<Derived>::Zero initialization problem

[Oleg Shirokobrod <oleg.shirokobrod@xxxxxxxxx>]

Hi Rasmus,

You are right. This abbreviated declaration of Jet

template <typename T, int N>
struct Jet {
  enum { DIMENSION = N };
  using Scalar = T;

  // Default-construct "a" because otherwise this can lead to false errors about
  // uninitialized uses when other classes relying on default constructed T
  // (where T is a Jet<T, N>). This usually only happens in opt mode. Note that
  // the C++ standard mandates that e.g. default constructed doubles are
  // initialized to 0.0; see sections 8.5 of the C++03 standard.
  Jet() : a() { v.setConstant(Scalar()); }

  // Constructor from scalar: a + 0.
  explicit Jet(const T& value) {
    a = value;
    v.setConstant(Scalar());
  }

  // The scalar part.
  T a;

  // The infinitesimal part.
  Eigen::Matrix<T, N, 1> v;

};

It has default zero initialized CTOR and CTOR initializing Jet from floating value. Of course instead of using Mat::Zero() -> return Mat::Constant(0) I can use Mat::Constant(0.0).

ср, 22 июн. 2022 г. в 19:00, Rasmus Munk Larsen <rmlarsen@xxxxxxxxxx>:

BTW: What happens if you do Mat x = Mat::Zero(10.0); ? Perhaps conversion from double or float work, because those types are "differentiable", as opposed to int.

On Wed, Jun 22, 2022 at 5:13 AM Oleg Shirokobrod <oleg.shirokobrod@xxxxxxxxx> wrote:

Hi,

In the file CwiseNullaryOp.h the functions DenseBase<Derived>::Zero call function DenseBase<Derived>::Constant which uses Scalar(0) for zero-initialization. It gives compilation error for this line 

using Mat = Eigen::Matrix<std::complex<ceres::Jet<double, 3>>, -1, 1, 0, -1, 1>; 

Mat x = Mat::Zero(10);

Here ceres::Jet<double, 3> is autodif type in ceres-solver. The problem is that it is not always possible to make conversion from int. From the other side for non-class-type scalar values, Scalar() provides a temporary which is zero-initialized. It is likely that for custom numerical class types Scalar() provides zero-initialized temporary. This is the case for Jet. When I replaced 

return Constant(size, Scalar(0)); 

with 

return Constant(size, Scalar()); 

in all Zero and setZero functions, code was compiled without errors.

Best,

Oleg