mirror of
https://gitlab.com/libeigen/eigen.git
synced 2024-12-15 07:10:37 +08:00
83 lines
2.9 KiB
Plaintext
83 lines
2.9 KiB
Plaintext
|
namespace Eigen {
|
||
|
|
|
||
|
|
/** \eigenManualPage TutorialReshape Reshape
|
||
|
|
|
||
|
|
Since the version 3.4, %Eigen exposes convenient methods to reshape a matrix to another matrix of different sizes or vector.
|
||
|
|
All cases are handled via the DenseBase::reshaped(NRowsType,NColsType) and DenseBase::reshaped() functions.
|
||
|
|
Those functions do not perform in-place reshaping, but instead return a <i> view </i> on the input expression.
|
||
|
|
|
||
|
|
\eigenAutoToc
|
||
|
|
|
||
|
|
\section TutorialReshapeMat2Mat Reshaped 2D views
|
||
|
|
|
||
|
|
The more general reshaping transformation is handled via: `reshaped(nrows,ncols)`.
|
||
|
|
Here is an example reshaping a 4x4 matrix to a 2x8 one:
|
||
|
|
|
||
|
|
<table class="example">
|
||
|
|
<tr><th>Example:</th><th>Output:</th></tr>
|
||
|
|
<tr><td>
|
||
|
|
\include MatrixBase_reshaped_int_int.cpp
|
||
|
|
</td>
|
||
|
|
<td>
|
||
|
|
\verbinclude MatrixBase_reshaped_int_int.out
|
||
|
|
</td></tr></table>
|
||
|
|
|
||
|
|
By default, the input coefficients are always interpreted in column-major order regardless of the storage order of the input expression.
|
||
|
|
For more control on ordering, compile-time sizes, and automatic size deduction, please see de documentation of DenseBase::reshaped(NRowsType,NColsType) that contains all the details with many examples.
|
||
|
|
|
||
|
|
|
||
|
|
\section TutorialReshapeMat2Vec 1D linear views
|
||
|
|
|
||
|
|
A very common usage of reshaping is to create a 1D linear view over a given 2D matrix or expression.
|
||
|
|
In this case, sizes can be deduced and thus omitted as in the following example:
|
||
|
|
|
||
|
|
<table class="example">
|
||
|
|
<tr><th>Example:</th></tr>
|
||
|
|
<tr><td>
|
||
|
|
\include MatrixBase_reshaped_to_vector.cpp
|
||
|
|
</td></tr>
|
||
|
|
<tr><th>Output:</th></tr>
|
||
|
|
<tr><td>
|
||
|
|
\verbinclude MatrixBase_reshaped_to_vector.out
|
||
|
|
</td></tr></table>
|
||
|
|
|
||
|
|
This shortcut always returns a column vector and by default input coefficients are always interpreted in column-major order.
|
||
|
|
Again, see the documentation of DenseBase::reshaped() for more control on the ordering.
|
||
|
|
|
||
|
|
\section TutorialReshapeInPlace
|
||
|
|
|
||
|
|
The above examples create reshaped views, but what about reshaping inplace a given matrix?
|
||
|
|
Of course this task in only conceivable for matrix and arrays having runtime dimensions.
|
||
|
|
In many cases, this can be accomplished via PlainObjectBase::resize(Index,Index):
|
||
|
|
|
||
|
|
<table class="example">
|
||
|
|
<tr><th>Example:</th></tr>
|
||
|
|
<tr><td>
|
||
|
|
\include Tutorial_reshaped_vs_resize_1.cpp
|
||
|
|
</td></tr>
|
||
|
|
<tr><th>Output:</th></tr>
|
||
|
|
<tr><td>
|
||
|
|
\verbinclude Tutorial_reshaped_vs_resize_1.out
|
||
|
|
</td></tr></table>
|
||
|
|
|
||
|
|
However beware that unlike \c reshaped, the result of \c resize depends on the input storage order.
|
||
|
|
It thus behaves similarly to `reshaped<AutoOrder>`:
|
||
|
|
|
||
|
|
<table class="example">
|
||
|
|
<tr><th>Example:</th></tr>
|
||
|
|
<tr><td>
|
||
|
|
\include Tutorial_reshaped_vs_resize_2.cpp
|
||
|
|
</td></tr>
|
||
|
|
<tr><th>Output:</th></tr>
|
||
|
|
<tr><td>
|
||
|
|
\verbinclude Tutorial_reshaped_vs_resize_2.out
|
||
|
|
</td></tr></table>
|
||
|
|
|
||
|
|
Finally, assigning a reshaped matrix to itself is currently not supported and will result to undefined-behavior because of \link TopicAliasing aliasing \endlink.
|
||
|
|
The following is forbidden: \code A = A.reshaped(2,8); \endcode
|
||
|
|
This is OK: \code A = A.reshaped(2,8).eval(); \endcode
|
||
|
|
|
||
|
|
*/
|
||
|
|
|
||
|
|
}
|