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66 lines
1.9 KiB
Plaintext
66 lines
1.9 KiB
Plaintext
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namespace Eigen {
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/** \eigenManualPage TutorialReshapeSlicing Reshape and Slicing
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%Eigen does not expose convenient methods to take slices or to reshape a matrix yet.
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Nonetheless, such features can easily be emulated using the Map class.
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\eigenAutoToc
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\section TutorialReshape Reshape
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A reshape operation consists in modifying the sizes of a matrix while keeping the same coefficients.
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Instead of modifying the input matrix itself, which is not possible for compile-time sizes, the approach consist in creating a different \em view on the storage using class Map.
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Here is a typical example creating a 1D linear view of a matrix:
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<table class="example">
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<tr><th>Example:</th><th>Output:</th></tr>
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<tr><td>
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\include Tutorial_ReshapeMat2Vec.cpp
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</td>
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<td>
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\verbinclude Tutorial_ReshapeMat2Vec.out
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</td></tr></table>
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Remark how the storage order of the input matrix modifies the order of the coefficients in the linear view.
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Here is another example reshaping a 2x6 matrix to a 6x2 one:
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<table class="example">
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<tr><th>Example:</th><th>Output:</th></tr>
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<tr><td>
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\include Tutorial_ReshapeMat2Mat.cpp
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</td>
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<td>
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\verbinclude Tutorial_ReshapeMat2Mat.out
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</td></tr></table>
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\section TutorialSlicing Slicing
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Slicing consists in taking a set of rows, or columns, or elements, uniformly spaced within a matrix.
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Again, the class Map allows to easily mimic this feature.
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For instance, one can take skip every P elements in a vector:
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<table class="example">
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<tr><th>Example:</th><th>Output:</th></tr>
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<tr><td>
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\include Tutorial_SlicingVec.cpp
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</td>
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<td>
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\verbinclude Tutorial_SlicingVec.out
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</td></tr></table>
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One can olso take one column over three using an adequate outer-stride or inner-stride depending on the actual storage order:
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<table class="example">
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<tr><th>Example:</th><th>Output:</th></tr>
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<tr><td>
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\include Tutorial_SlicingCol.cpp
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</td>
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<td>
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\verbinclude Tutorial_SlicingCol.out
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</td></tr></table>
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*/
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}
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