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Add support for Eigen::Ref<...> function arguments

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Eigen::Ref is a common way to pass eigen dense types without needing a
template, e.g. the single definition `void
func(Eigen::Ref<Eigen::MatrixXd> x)` can be called with any double
matrix-like object.

The current pybind11 eigen support fails with internal errors if
attempting to bind a function with an Eigen::Ref<...> argument because
Eigen::Ref<...> satisfies the "is_eigen_dense" requirement, but can't
compile if actually used: Eigen::Ref<...> itself is not default
constructible, and so the argument std::tuple containing an
Eigen::Ref<...> isn't constructible, which results in compilation
failure.

This commit adds support for Eigen::Ref<...> by giving it its own
type_caster implementation which consists of an internal type_caster of
the referenced type, load/cast methods that dispatch to the internal
type_caster, and a unique_ptr to an Eigen::Ref<> instance that gets
set during load().

There is, of course, no performance advantage for pybind11-using code of
using Eigen::Ref<...>--we are allocating a matrix of the derived type
when loading it--but this has the advantage of allowing pybind11 to bind
transparently to C++ methods taking Eigen::Refs.
This commit is contained in:
Jason Rhinelander
2016-08-03 16:50:22 -04:00
parent 7f9603fe24
commit 5fd5074a0b
4 changed files with 63 additions and 1 deletions
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15
example/eigen.cpp
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@@ -9,6 +9,7 @@
#include "example.h"
#include <pybind11/eigen.h>
#include <Eigen/Cholesky>
Eigen::VectorXf double_col(const Eigen::VectorXf& x)
{ return 2.0f * x; }
@@ -19,6 +20,14 @@ Eigen::RowVectorXf double_row(const Eigen::RowVectorXf& x)
Eigen::MatrixXf double_mat_cm(const Eigen::MatrixXf& x)
{ return 2.0f * x; }
// Different ways of passing via Eigen::Ref; the first and second are the Eigen-recommended
Eigen::MatrixXd cholesky1(Eigen::Ref<Eigen::MatrixXd> &x) { return x.llt().matrixL(); }
Eigen::MatrixXd cholesky2(const Eigen::Ref<const Eigen::MatrixXd> &x) { return x.llt().matrixL(); }
Eigen::MatrixXd cholesky3(const Eigen::Ref<Eigen::MatrixXd> &x) { return x.llt().matrixL(); }
Eigen::MatrixXd cholesky4(Eigen::Ref<const Eigen::MatrixXd> &x) { return x.llt().matrixL(); }
Eigen::MatrixXd cholesky5(Eigen::Ref<Eigen::MatrixXd> x) { return x.llt().matrixL(); }
Eigen::MatrixXd cholesky6(Eigen::Ref<const Eigen::MatrixXd> x) { return x.llt().matrixL(); }
typedef Eigen::Matrix<float, Eigen::Dynamic, Eigen::Dynamic, Eigen::RowMajor> MatrixXfRowMajor;
MatrixXfRowMajor double_mat_rm(const MatrixXfRowMajor& x)
{ return 2.0f * x; }
@@ -40,6 +49,12 @@ void init_eigen(py::module &m) {
m.def("double_row", &double_row);
m.def("double_mat_cm", &double_mat_cm);
m.def("double_mat_rm", &double_mat_rm);
m.def("cholesky1", &cholesky1);
m.def("cholesky2", &cholesky2);
m.def("cholesky3", &cholesky3);
m.def("cholesky4", &cholesky4);
m.def("cholesky5", &cholesky5);
m.def("cholesky6", &cholesky6);
m.def("fixed_r", [mat]() -> FixedMatrixR {
return FixedMatrixR(mat);