Page 54 - Basics of MATLAB and Beyond

i =
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i =
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Vectorised Code

matlab is a matrix language, and many of its algorithms are optimised
for matrices. matlab code can often be accelerated by replacing for
and while loops with operations on matrices. In the following example,
we calculate the factorial of the numbers from 1 to 500 using a for
loop. Create a script m-file called factorialloop.m that contains the
following code:

for number = 1:500
fact = 1;
for i = 2:number
fact = fact*i;
end
y(number) = fact;
end
We can time how long this program takes to run by using the stopwatch
functions tic and toc:

>> tic;factorialloop;toc
elapsed_time =
4.6332
which is the time in seconds. The same calculation can be done in much
less time by replacing the internal for loop by the prod function. Create
an m-file called factorialvect.m:
for number = 1:500
y(number) = prod(1:number);
end

This version takes about a tenth of the time:
>> clear
>> tic;factorialvect;toc
elapsed_time =
0.4331

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