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<h4 class="subsection">20.1.1 Creating Diagonal Matrices</h4>
<p>The most common and easiest way to create a diagonal matrix is using the built-in
function <dfn>diag</dfn>. The expression <code>diag (v)</code>, with <var>v</var> a vector,
will create a square diagonal matrix with elements on the main diagonal given
by the elements of <var>v</var>, and size equal to the length of <var>v</var>.
<code>diag (v, m, n)</code> can be used to construct a rectangular diagonal matrix.
The result of these expressions will be a special diagonal matrix object, rather
than a general matrix object.
<p>Diagonal matrix with unit elements can be created using <dfn>eye</dfn>.
Some other built-in functions can also return diagonal matrices. Examples include
<dfn>balance</dfn> or <dfn>inv</dfn>.
<p>Example:
<pre class="example"> diag (1:4)
Diagonal Matrix
1 0 0 0
0 2 0 0
0 0 3 0
0 0 0 4
diag(1:3,5,3)
Diagonal Matrix
1 0 0
0 2 0
0 0 3
0 0 0
0 0 0
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