In this exercise, we time some methods for multiplying a lower
triangular matrix by its transpose.
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<li>
Run these Matlab commands: <br>
L = tril(rand(250)); <br>
tic <br>
A = L*L'; <br>
t1 = toc <br>
<li>
Now write either a row-oriented algorithm to compute  B = L L' or
a column-oriented algorithm.
<li>
Run your algorithm and compare the time with t1.
<li>
If you want to verify the correctness of your algorithm, 
see if <br>
norm(A-B) <br>
is small.
<li>
Algorithm MatMatDot (p180) and MatMatSax (p181) can be used 
to help you design your algorithm.  Just modify them so
that they don't touch any zeros in the matrix L.
<li>
Send a plain-text email with a copy of your program and
its output by midnight on Monday.
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