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