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<title>Creating row and column views - GNU Scientific Library -- Reference Manual</title>
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<h4 class="subsection">8.4.6 Creating row and column views</h4>
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<p>In general there are two ways to access an object, by reference or by
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copying. The functions described in this section create vector views
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which allow access to a row or column of a matrix by reference.
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Modifying elements of the view is equivalent to modifying the matrix,
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since both the vector view and the matrix point to the same memory
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— Function: gsl_vector_view <b>gsl_matrix_row</b> (<var>gsl_matrix * m, size_t i</var>)<var><a name="index-gsl_005fmatrix_005frow-913"></a></var><br>
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— Function: gsl_vector_const_view <b>gsl_matrix_const_row</b> (<var>const gsl_matrix * m, size_t i</var>)<var><a name="index-gsl_005fmatrix_005fconst_005frow-914"></a></var><br>
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<blockquote><p>These functions return a vector view of the <var>i</var>-th row of the matrix
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<var>m</var>. The <code>data</code> pointer of the new vector is set to null if
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<var>i</var> is out of range.
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<p>The function <code>gsl_vector_const_row</code> is equivalent to
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<code>gsl_matrix_row</code> but can be used for matrices which are declared
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</p></blockquote></div>
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— Function: gsl_vector_view <b>gsl_matrix_column</b> (<var>gsl_matrix * m, size_t j</var>)<var><a name="index-gsl_005fmatrix_005fcolumn-915"></a></var><br>
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— Function: gsl_vector_const_view <b>gsl_matrix_const_column</b> (<var>const gsl_matrix * m, size_t j</var>)<var><a name="index-gsl_005fmatrix_005fconst_005fcolumn-916"></a></var><br>
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<blockquote><p>These functions return a vector view of the <var>j</var>-th column of the
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matrix <var>m</var>. The <code>data</code> pointer of the new vector is set to
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null if <var>j</var> is out of range.
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<p>The function <code>gsl_vector_const_column</code> is equivalent to
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<code>gsl_matrix_column</code> but can be used for matrices which are declared
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</p></blockquote></div>
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<p><a name="index-matrix-diagonal-917"></a><a name="index-diagonal_002c-of-a-matrix-918"></a>
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— Function: gsl_vector_view <b>gsl_matrix_diagonal</b> (<var>gsl_matrix * m</var>)<var><a name="index-gsl_005fmatrix_005fdiagonal-919"></a></var><br>
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— Function: gsl_vector_const_view <b>gsl_matrix_const_diagonal</b> (<var>const gsl_matrix * m</var>)<var><a name="index-gsl_005fmatrix_005fconst_005fdiagonal-920"></a></var><br>
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<blockquote><p>These functions returns a vector view of the diagonal of the matrix
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<var>m</var>. The matrix <var>m</var> is not required to be square. For a
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rectangular matrix the length of the diagonal is the same as the smaller
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dimension of the matrix.
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<p>The function <code>gsl_matrix_const_diagonal</code> is equivalent to
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<code>gsl_matrix_diagonal</code> but can be used for matrices which are
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declared <code>const</code>.
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</p></blockquote></div>
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<p><a name="index-matrix-subdiagonal-921"></a><a name="index-subdiagonal_002c-of-a-matrix-922"></a>
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— Function: gsl_vector_view <b>gsl_matrix_subdiagonal</b> (<var>gsl_matrix * m, size_t k</var>)<var><a name="index-gsl_005fmatrix_005fsubdiagonal-923"></a></var><br>
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— Function: gsl_vector_const_view <b>gsl_matrix_const_subdiagonal</b> (<var>const gsl_matrix * m, size_t k</var>)<var><a name="index-gsl_005fmatrix_005fconst_005fsubdiagonal-924"></a></var><br>
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<blockquote><p>These functions return a vector view of the <var>k</var>-th subdiagonal of
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the matrix <var>m</var>. The matrix <var>m</var> is not required to be square.
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The diagonal of the matrix corresponds to k = 0.
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<p>The function <code>gsl_matrix_const_subdiagonal</code> is equivalent to
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<code>gsl_matrix_subdiagonal</code> but can be used for matrices which are
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declared <code>const</code>.
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</p></blockquote></div>
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<p><a name="index-matrix-superdiagonal-925"></a><a name="index-superdiagonal_002c-matrix-926"></a>
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— Function: gsl_vector_view <b>gsl_matrix_superdiagonal</b> (<var>gsl_matrix * m, size_t k</var>)<var><a name="index-gsl_005fmatrix_005fsuperdiagonal-927"></a></var><br>
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— Function: gsl_vector_const_view <b>gsl_matrix_const_superdiagonal</b> (<var>const gsl_matrix * m, size_t k</var>)<var><a name="index-gsl_005fmatrix_005fconst_005fsuperdiagonal-928"></a></var><br>
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<blockquote><p>These functions return a vector view of the <var>k</var>-th superdiagonal of
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the matrix <var>m</var>. The matrix <var>m</var> is not required to be square. The
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diagonal of the matrix corresponds to k = 0.
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<p>The function <code>gsl_matrix_const_superdiagonal</code> is equivalent to
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<code>gsl_matrix_superdiagonal</code> but can be used for matrices which are
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declared <code>const</code>.
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</p></blockquote></div>
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<!-- @deftypefun {gsl_vector *} gsl_vector_alloc_row_from_matrix (gsl_matrix * @var{m}, size_t @var{i}) -->
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<!-- This function allocates a new @code{gsl_vector} struct which points to -->
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<!-- the @var{i}-th row of the matrix @var{m}. -->
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<!-- @end deftypefun -->
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<!-- @deftypefun {gsl_vector *} gsl_vector_alloc_col_from_matrix (gsl_matrix * @var{m}, size_t @var{j}) -->
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<!-- This function allocates a new @code{gsl_vector} struct which points to -->
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<!-- the @var{j}-th column of the matrix @var{m}. -->
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<!-- @end deftypefun -->
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