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<h2 class="chapter">4 Numeric Data Types</h2>
<p><a name="index-numeric-constant-211"></a><a name="index-numeric-value-212"></a>
A <dfn>numeric constant</dfn> may be a scalar, a vector, or a matrix, and it
may contain complex values.
<p>The simplest form of a numeric constant, a scalar, is a single number
that can be an integer, a decimal fraction, a number in scientific
(exponential) notation, or a complex number. Note that by default numeric
constants are represented within Octave in double-precision floating
point format (complex constants are stored as pairs of double-precision
floating point values). It is however possible to represent real
integers as described in <a href="Integer-Data-Types.html#Integer-Data-Types">Integer Data Types</a>. Here are some
examples of real-valued numeric constants, which all have the same
value:
<pre class="example"> 105
1.05e+2
1050e-1
</pre>
<p>To specify complex constants, you can write an expression of the form
<pre class="example"> 3 + 4i
3.0 + 4.0i
0.3e1 + 40e-1i
</pre>
<p class="noindent">all of which are equivalent. The letter ‘<samp><span class="samp">i</span></samp>’ in the previous example
stands for the pure imaginary constant, defined as
<code>sqrt (-1)</code>.
<p>For Octave to recognize a value as the imaginary part of a complex
constant, a space must not appear between the number and the ‘<samp><span class="samp">i</span></samp>’.
If it does, Octave will print an error message, like this:
<pre class="example"> octave:13> 3 + 4 i
parse error:
syntax error
>>> 3 + 4 i
^
</pre>
<p class="noindent">You may also use ‘<samp><span class="samp">j</span></samp>’, ‘<samp><span class="samp">I</span></samp>’, or ‘<samp><span class="samp">J</span></samp>’ in place of the
‘<samp><span class="samp">i</span></samp>’ above. All four forms are equivalent.
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<p><a name="doc_002ddouble"></a>
<div class="defun">
— Built-in Function: <b>double</b> (<var>x</var>)<var><a name="index-double-213"></a></var><br>
<blockquote><p>Convert <var>x</var> to double precision type.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dsingle.html#doc_002dsingle">single</a>.
</p></blockquote></div>
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<p><a name="doc_002dcomplex"></a>
<div class="defun">
— Built-in Function: <b>complex</b> (<var>x</var>)<var><a name="index-complex-214"></a></var><br>
— Built-in Function: <b>complex</b> (<var>re, im</var>)<var><a name="index-complex-215"></a></var><br>
<blockquote><p>Return a complex result from real arguments. With 1 real argument <var>x</var>,
return the complex result <var>x</var><code> + 0i</code>. With 2 real arguments,
return the complex result <var>re</var><code> + </code><var>im</var>. <code>complex</code> can
often be more convenient than expressions such as <code>a + i*b</code>.
For example:
<pre class="example"> complex ([1, 2], [3, 4])
⇒
1 + 3i 2 + 4i
</pre>
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dreal.html#doc_002dreal">real</a>, <a href="doc_002dimag.html#doc_002dimag">imag</a>, <a href="doc_002discomplex.html#doc_002discomplex">iscomplex</a>.
</p></blockquote></div>
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