 <p>MATLAB 7.0 provides the <code>NTHROOT</code> function, which returns the real roots of a number. So your formula becomes <code>NTHROOT(-8, 3) = -2</code></p> <p>If you are using a version prior to MATLAB 7.0 (R14), please read the following:</p> <p>To obtain the real cube root of a negative real number "x", rather than executing:</p> <pre><code>x.^(1/3) </code></pre> <p>use the command:</p> <pre><code>sign(x).*abs(x.^(1/3)) </code></pre> <p>This will find the absolute value of the root and modify it by the sign of the argument.</p> <p><a href="http://www.mathworks.com.au/support/solutions/en/data/1-15M1N/index.html?product=ML&amp;solution=1-15M1N" rel="nofollow">See this</a></p>