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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>
<p>In general there are two ways to access an object, by reference or by
copying. The functions described in this section create vector views
which allow access to a row or column of a matrix by reference.
Modifying elements of the view is equivalent to modifying the matrix,
since both the vector view and the matrix point to the same memory
block.
<div class="defun">
— Function: gsl_vector_view <b>gsl_matrix_row</b> (<var>gsl_matrix * m, size_t i</var>)<var><a name="index-gsl_005fmatrix_005frow-983"></a></var><br>
— 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-984"></a></var><br>
<blockquote><p>These functions return a vector view of the <var>i</var>-th row of the matrix
<var>m</var>. The <code>data</code> pointer of the new vector is set to null if
<var>i</var> is out of range.
<p>The function <code>gsl_vector_const_row</code> is equivalent to
<code>gsl_matrix_row</code> but can be used for matrices which are declared
<code>const</code>.
</p></blockquote></div>
<div class="defun">
— Function: gsl_vector_view <b>gsl_matrix_column</b> (<var>gsl_matrix * m, size_t j</var>)<var><a name="index-gsl_005fmatrix_005fcolumn-985"></a></var><br>
— 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-986"></a></var><br>
<blockquote><p>These functions return a vector view of the <var>j</var>-th column of the
matrix <var>m</var>. The <code>data</code> pointer of the new vector is set to
null if <var>j</var> is out of range.
<p>The function <code>gsl_vector_const_column</code> is equivalent to
<code>gsl_matrix_column</code> but can be used for matrices which are declared
<code>const</code>.
</p></blockquote></div>
<div class="defun">
— Function: gsl_vector_view <b>gsl_matrix_subrow</b> (<var>gsl_matrix * m, size_t i, size_t offset, size_t n</var>)<var><a name="index-gsl_005fmatrix_005fsubrow-987"></a></var><br>
— Function: gsl_vector_const_view <b>gsl_matrix_const_subrow</b> (<var>const gsl_matrix * m, size_t i, size_t offset, size_t n</var>)<var><a name="index-gsl_005fmatrix_005fconst_005fsubrow-988"></a></var><br>
<blockquote><p>These functions return a vector view of the <var>i</var>-th row of the matrix
<var>m</var> beginning at <var>offset</var> elements past the first column and
containing <var>n</var> elements. The <code>data</code> pointer of the new vector
is set to null if <var>i</var>, <var>offset</var>, or <var>n</var> are out of range.
<p>The function <code>gsl_vector_const_subrow</code> is equivalent to
<code>gsl_matrix_subrow</code> but can be used for matrices which are declared
<code>const</code>.
</p></blockquote></div>
<div class="defun">
— Function: gsl_vector_view <b>gsl_matrix_subcolumn</b> (<var>gsl_matrix * m, size_t j, size_t offset, size_t n</var>)<var><a name="index-gsl_005fmatrix_005fsubcolumn-989"></a></var><br>
— Function: gsl_vector_const_view <b>gsl_matrix_const_subcolumn</b> (<var>const gsl_matrix * m, size_t j, size_t offset, size_t n</var>)<var><a name="index-gsl_005fmatrix_005fconst_005fsubcolumn-990"></a></var><br>
<blockquote><p>These functions return a vector view of the <var>j</var>-th column of the matrix
<var>m</var> beginning at <var>offset</var> elements past the first row and
containing <var>n</var> elements. The <code>data</code> pointer of the new vector
is set to null if <var>j</var>, <var>offset</var>, or <var>n</var> are out of range.
<p>The function <code>gsl_vector_const_subcolumn</code> is equivalent to
<code>gsl_matrix_subcolumn</code> but can be used for matrices which are declared
<code>const</code>.
</p></blockquote></div>
<p><a name="index-matrix-diagonal-991"></a><a name="index-diagonal_002c-of-a-matrix-992"></a>
<div class="defun">
— Function: gsl_vector_view <b>gsl_matrix_diagonal</b> (<var>gsl_matrix * m</var>)<var><a name="index-gsl_005fmatrix_005fdiagonal-993"></a></var><br>
— 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-994"></a></var><br>
<blockquote><p>These functions return a vector view of the diagonal of the matrix
<var>m</var>. The matrix <var>m</var> is not required to be square. For a
rectangular matrix the length of the diagonal is the same as the smaller
dimension of the matrix.
<p>The function <code>gsl_matrix_const_diagonal</code> is equivalent to
<code>gsl_matrix_diagonal</code> but can be used for matrices which are
declared <code>const</code>.
</p></blockquote></div>
<p><a name="index-matrix-subdiagonal-995"></a><a name="index-subdiagonal_002c-of-a-matrix-996"></a>
<div class="defun">
— Function: gsl_vector_view <b>gsl_matrix_subdiagonal</b> (<var>gsl_matrix * m, size_t k</var>)<var><a name="index-gsl_005fmatrix_005fsubdiagonal-997"></a></var><br>
— 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-998"></a></var><br>
<blockquote><p>These functions return a vector view of the <var>k</var>-th subdiagonal of
the matrix <var>m</var>. The matrix <var>m</var> is not required to be square.
The diagonal of the matrix corresponds to k = 0.
<p>The function <code>gsl_matrix_const_subdiagonal</code> is equivalent to
<code>gsl_matrix_subdiagonal</code> but can be used for matrices which are
declared <code>const</code>.
</p></blockquote></div>
<p><a name="index-matrix-superdiagonal-999"></a><a name="index-superdiagonal_002c-matrix-1000"></a>
<div class="defun">
— Function: gsl_vector_view <b>gsl_matrix_superdiagonal</b> (<var>gsl_matrix * m, size_t k</var>)<var><a name="index-gsl_005fmatrix_005fsuperdiagonal-1001"></a></var><br>
— 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-1002"></a></var><br>
<blockquote><p>These functions return a vector view of the <var>k</var>-th superdiagonal of
the matrix <var>m</var>. The matrix <var>m</var> is not required to be square. The
diagonal of the matrix corresponds to k = 0.
<p>The function <code>gsl_matrix_const_superdiagonal</code> is equivalent to
<code>gsl_matrix_superdiagonal</code> but can be used for matrices which are
declared <code>const</code>.
</p></blockquote></div>
<!-- @deftypefun {gsl_vector *} gsl_vector_alloc_row_from_matrix (gsl_matrix * @var{m}, size_t @var{i}) -->
<!-- This function allocates a new @code{gsl_vector} struct which points to -->
<!-- the @var{i}-th row of the matrix @var{m}. -->
<!-- @end deftypefun -->
<!-- @deftypefun {gsl_vector *} gsl_vector_alloc_col_from_matrix (gsl_matrix * @var{m}, size_t @var{j}) -->
<!-- This function allocates a new @code{gsl_vector} struct which points to -->
<!-- the @var{j}-th column of the matrix @var{m}. -->
<!-- @end deftypefun -->
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