Explanation of the assertion on unaligned arrays

Hello! You are seeing this webpage because your program terminated on an assertion failure like this one:
my_program: path/to/eigen2/Eigen/src/Core/MatrixStorage.h:44:
Eigen::ei_matrix_array<T, Size, MatrixOptions, Align>::ei_matrix_array()
[with T = double, int Size = 2, int MatrixOptions = 2, bool Align = true]:
Assertion `(reinterpret_cast<size_t>(array) & 0xf) == 0 && "this assertion
is explained here: http://eigen.tuxfamily.org/dox/UnalignedArrayAssert.html
 READ THIS WEB PAGE !!! ****"' failed.

There are 3 known causes for this issue. Please read on to understand them and learn how to fix them.

Table of contents

Cause 1: Structures having Eigen objects as members

If you have code like this,

class Foo
{
  //...
  Eigen::Vector2d v;
  //...
};
//...
Foo *foo = new Foo;

then you need to read this separate page: Structures Having Eigen Members.

Note that here, Eigen::Vector2d is only used as an example, more generally the issue arises for all fixed-size vectorizable Eigen types.

Cause 2: STL Containers

If you use STL Containers such as std::vector, std::map, ..., with Eigen objects, like this,

std::vector<Eigen::Matrix2f> my_vector;
std::map<int, Eigen::Matrix2f> my_map;

then you need to read this separate page: Using STL Containers with Eigen.

Note that here, Eigen::Matrix2f is only used as an example, more generally the issue arises for all fixed-size vectorizable Eigen types.

Cause 3: Passing Eigen objects by value

If some function in your code is getting an Eigen object passed by value, like this,

void func(Eigen::Vector4d v);

then you need to read this separate page: Passing Eigen objects by value to functions.

Note that here, Eigen::Vector4d is only used as an example, more generally the issue arises for all fixed-size vectorizable Eigen types.

Explanation

fixed-size vectorizable Eigen objects must absolutely be created at 16-byte-aligned locations, otherwise SIMD instructions adressing them will crash.

Eigen normally takes care of these alignment issues for you, by setting an alignment attribute on them and by overloading their "operator new".

However there are a few corner cases where these alignment settings get overridden: they are the possible causes for this assertion.


Generated on Thu Apr 9 10:10:01 2009 for Eigen by  doxygen 1.5.5