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</pre><pre class="codeoutput">Elapsed time is 0.638810 seconds.
Elapsed time is 0.813682 seconds.
Elapsed time is 0.317389 seconds.
Elapsed time is 0.319094 seconds.
</pre><h2>Least-squares problems<a name="13"></a></h2>
         <p>Here are some different methods for solving a least-squares problem when your system is over-determined.  The last two methods
            are the same.
         </p><pre class="codeinput">A = rand (1000,200) ;
b = rand (1000,1) ;

tic ; x = A\b            ; toc, norm (A'*A*