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<h4 class="subsection">4.1.1 Empty Matrices</h4>
<p>A matrix may have one or both dimensions zero, and operations on empty
matrices are handled as described by Carl de Boor in <cite>An Empty
Exercise</cite>, SIGNUM, Volume 25, pages 2-6, 1990 and C. N. Nett and W. M.
Haddad, in <cite>A System-Theoretic Appropriate Realization of the Empty
Matrix Concept</cite>, IEEE Transactions on Automatic Control, Volume 38,
Number 5, May 1993.
Briefly, given a scalar <var>s</var>, an <var>m</var> by
<var>n</var> matrix <code>M(mxn)</code>, and an <var>m</var> by <var>n</var> empty matrix
<code>[](mxn)</code> (with either one or both dimensions equal to zero), the
following are true:
<pre class="example"> s * [](mxn) = [](mxn) * s = [](mxn)
[](mxn) + [](mxn) = [](mxn)
[](0xm) * M(mxn) = [](0xn)
M(mxn) * [](nx0) = [](mx0)
[](mx0) * [](0xn) = 0(mxn)
</pre>
<p>By default, dimensions of the empty matrix are printed along with the
empty matrix symbol, ‘<samp><span class="samp">[]</span></samp>’. The built-in variable
<code>print_empty_dimensions</code> controls this behavior.
<!-- print_empty_dimensions src/pr-output.cc -->
<p><a name="doc_002dprint_005fempty_005fdimensions"></a>
<div class="defun">
— Built-in Function: <var>val</var> = <b>print_empty_dimensions</b> ()<var><a name="index-print_005fempty_005fdimensions-264"></a></var><br>
— Built-in Function: <var>old_val</var> = <b>print_empty_dimensions</b> (<var>new_val</var>)<var><a name="index-print_005fempty_005fdimensions-265"></a></var><br>
— Built-in Function: <b>print_empty_dimensions</b> (<var>new_val, "local"</var>)<var><a name="index-print_005fempty_005fdimensions-266"></a></var><br>
<blockquote><p>Query or set the internal variable that controls whether the
dimensions of empty matrices are printed along with the empty matrix
symbol, ‘<samp><span class="samp">[]</span></samp>’. For example, the expression
<pre class="example"> zeros (3, 0)
</pre>
<p class="noindent">will print
<pre class="example"> ans = [](3x0)
</pre>
<p>When called from inside a function with the "local" option, the variable is
changed locally for the function and any subroutines it calls. The original
variable value is restored when exiting the function.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dformat.html#doc_002dformat">format</a>.
</p></blockquote></div>
<p>Empty matrices may also be used in assignment statements as a convenient
way to delete rows or columns of matrices.
See <a href="Assignment-Ops.html#Assignment-Ops">Assignment Expressions</a>.
<p>When Octave parses a matrix expression, it examines the elements of the
list to determine whether they are all constants. If they are, it
replaces the list with a single matrix constant.
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