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diff --git a/doc/A05_PortingFrom2To3.dox b/doc/A05_PortingFrom2To3.dox new file mode 100644 index 000000000..4425cc0e0 --- /dev/null +++ b/doc/A05_PortingFrom2To3.dox @@ -0,0 +1,73 @@ +namespace Eigen { + +/** \page Eigen2ToEigen3 Porting from Eigen2 to Eigen3 + +The goals of this page is to enumerate the API changes between Eigen2 and Eigen3, +and to help porting an application from Eigen2 to Eigen3. + +\b Table \b of \b contents + - \ref summary + - \ref modules + - \ref core + +\section CompatibilitySupport Eigen2 compatibility support + +In order to ease th switch from Eigen2 to Eigen3, Eigen3 features a compatibility mode which can be enabled by defining the EIGEN2_SUPPORT preprocessor token \b before including any Eigen's header (typically it should be set in your project options). + +\section ChangeList List of changes + +<table> +<tr><td>Eigen 2</td><td>Eigen 3</td></tr> +<tr><td>vec.start(length)</td><td>vec.head(length)</td></tr> +<tr><td>vec.start<length>()</td><td>vec.head<length>()</td></tr> +<tr><td>vec.end(length)</td><td>vec.tail(length)</td></tr> +<tr><td>vec.end<length>()</td><td>vec.tail<length>()</td></tr> +<tr></tr> +<tr><td>mat.cwise().XXX()</td><td>mat.array().XXX() \redstar</td></tr> +<tr></tr> +<tr><td>\code c = (a * b).lazy();\endcode</td><td>\code c.noalias() = a * b;\endcode</td></tr> +</table> + +\redstar See \ref CoefficientWiseOperations for details. + +\section CoefficientWiseOperations Coefficient wise operations + +In Eigen2, coefficient wise operations which have no proper mathematical definiton (as a coeff wise product) +were achied using the .cwise() prefix, e.g.: +\code a.cwise() * b \code +In Eigen3 this .cwise() prefix has been supersed by a new kind of matrix type called +Array for which all operations are performed coefficient wise. You can easily view a matrix as an array and vice versa using +the MatrixBase::array() and ArrayBase::matrix() functions respectively. Here is an example: +\code +Vector4f a, b, c; +c = a.array() * b.array(); +\endcode +Note that the .array() function is not at all a synonym of the deprecated .cwise() prefix. +While the .cwise() prefix changed the behavior of the following operator, the array() function performs +a permanent convertion to the array world. Therefore, for binary operations such as the coeff wise product, +both sides must be converted to an \em array as in the above example. On the other hand, when you +concatenates multiple coeff wise operations you only have to do the conversion once, e.g.: +\code +Vector4f a, b, c; +c = a.array().abs().pow(3) * b.array().abs().sin(); +\endcode +With Eigen2 you would have written: +\code +c = (a.cwise().abs().cwise().pow(3)).cwise() * (b.cwise().abs().cwise().sin()); +\endcode + +\section LazyVsNoalias Lazy evaluation versus noalias + +In Eigen all operations are performed in a lazy fashion expected the matrix products which are always evaluated to a temporary by default. +In Eigen2, lazy evaluation could be enforced by tagging a product using the .lazy() function. However, in complex expressions it was not +easy to determine where to put the lazy() function. In Eigen3, the lazy() feature has been supersed by the MatrixBase::noalias() function +which can be used on the left hand side of an assignment when no aliasing can occur. Here is an example: +\code +MatrixXf a, b, c; +... +c.noalias() += 2 * a.transpose() * b; +\endcode + +*/ + +} |