<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <!-- Created by GNU Texinfo 6.5, http://www.gnu.org/software/texinfo/ --> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <title>Empty Matrices (GNU Octave (version 5.1.0))</title> <meta name="description" content="Empty Matrices (GNU Octave (version 5.1.0))"> <meta name="keywords" content="Empty Matrices (GNU Octave (version 5.1.0))"> <meta name="resource-type" content="document"> <meta name="distribution" content="global"> <meta name="Generator" content="makeinfo"> <link href="index.html#Top" rel="start" title="Top"> <link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index"> <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> <link href="Matrices.html#Matrices" rel="up" title="Matrices"> <link href="Ranges.html#Ranges" rel="next" title="Ranges"> <link href="Matrices.html#Matrices" rel="prev" title="Matrices"> <style type="text/css"> <!-- a.summary-letter {text-decoration: none} blockquote.indentedblock {margin-right: 0em} blockquote.smallindentedblock {margin-right: 0em; font-size: smaller} blockquote.smallquotation {font-size: smaller} div.display {margin-left: 3.2em} div.example {margin-left: 3.2em} div.lisp {margin-left: 3.2em} div.smalldisplay {margin-left: 3.2em} div.smallexample {margin-left: 3.2em} div.smalllisp {margin-left: 3.2em} kbd {font-style: oblique} pre.display {font-family: inherit} pre.format {font-family: inherit} pre.menu-comment {font-family: serif} pre.menu-preformatted {font-family: serif} pre.smalldisplay {font-family: inherit; font-size: smaller} pre.smallexample {font-size: smaller} pre.smallformat {font-family: inherit; font-size: smaller} pre.smalllisp {font-size: smaller} span.nolinebreak {white-space: nowrap} span.roman {font-family: initial; font-weight: normal} span.sansserif {font-family: sans-serif; font-weight: normal} ul.no-bullet {list-style: none} --> </style> <link rel="stylesheet" type="text/css" href="octave.css"> </head> <body lang="en"> <a name="Empty-Matrices"></a> <div class="header"> <p> Up: <a href="Matrices.html#Matrices" accesskey="u" rel="up">Matrices</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> </div> <hr> <a name="Empty-Matrices-1"></a> <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: </p> <div class="example"> <pre class="example">s * [](mxn) = [](mxn) * s = [](mxn) [](mxn) + [](mxn) = [](mxn) [](0xm) * M(mxn) = [](0xn) M(mxn) * [](nx0) = [](mx0) [](mx0) * [](0xn) = 0(mxn) </pre></div> <p>By default, dimensions of the empty matrix are printed along with the empty matrix symbol, ‘<samp>[]</samp>’. The built-in variable <code>print_empty_dimensions</code> controls this behavior. </p> <a name="XREFprint_005fempty_005fdimensions"></a><dl> <dt><a name="index-print_005fempty_005fdimensions"></a><em><var>val</var> =</em> <strong>print_empty_dimensions</strong> <em>()</em></dt> <dt><a name="index-print_005fempty_005fdimensions-1"></a><em><var>old_val</var> =</em> <strong>print_empty_dimensions</strong> <em>(<var>new_val</var>)</em></dt> <dt><a name="index-print_005fempty_005fdimensions-2"></a><em></em> <strong>print_empty_dimensions</strong> <em>(<var>new_val</var>, "local")</em></dt> <dd><p>Query or set the internal variable that controls whether the dimensions of empty matrices are printed along with the empty matrix symbol, ‘<samp>[]</samp>’. </p> <p>For example, the expression </p> <div class="example"> <pre class="example">zeros (3, 0) </pre></div> <p>will print </p> <div class="example"> <pre class="example">ans = [](3x0) </pre></div> <p>When called from inside a function with the <code>"local"</code> option, the variable is changed locally for the function and any subroutines it calls. The original variable value is restored when exiting the function. </p> <p><strong>See also:</strong> <a href="Terminal-Output.html#XREFformat">format</a>. </p></dd></dl> <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> <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. </p> <hr> <div class="header"> <p> Up: <a href="Matrices.html#Matrices" accesskey="u" rel="up">Matrices</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> </div> </body> </html>