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©2009 by L. Lagerstrom
Nested Loops
• For an introduction to the basic concepts, see the
associated video clip
• Nested loop structure
• Nested loop results
• Nested loop execution
• Nested loop example
• Finding the location of the max value in an array
• The indmax function
©2009 by L. Lagerstrom
The Nested Loop Structure
Often it's useful to put one loop inside another loop. We call this a
double loop, or a nested loop. The basic structure is:
for m = 1:3
for n = 1:4
fprintf('Value of m is %.0f
and value of n is %.0f \n', m, n)
end
end
See if you can figure out what will be displayed when this code is run.
(We give the results on the next slide.)
©2009 by L. Lagerstrom
Nested Loop Results
Our nested loop example:
for m = 1:3
for n = 1:4
fprintf('Value of m is %.0f
and value of n is %.0f \n', m, n)
end
end
The displayed results will be:
Value of m is 1 and value of n is 1
Value of m is 1 and value of n is 2
Value of m is 1 and value of n is 3
Value of m is 1 and value of n is 4
Value of m is 2 and value of n is 1
Value of m is 2 and value of n is 2
Value of m is 2 and value of n is 3
[etc., etc.]
Value of m is 3 and value of n is 4
©2009 by L. Lagerstrom
Nested Loop Execution
From the loop code, and/or from the displayed results on the previous
slide, we see that the loops execute as follows:
1. Matlab sets m to a value of 1 and starts the outer loop.
2. Once inside the outer loop, Matlab finds the inner loop. So it
sets n to 1 and starts the inner loop.
3. The inner loop executes completely, meaning, in this case, that
it iterates 4 times, displaying the "Value of.
.." message each time. The
value of the inner loop variable (n) changes each time, but the value of
m (from the outer loop) does not.
4. When the inner loop is done, Matlab proceeds and finds that it
is at the end of the first iteration of the outer loop. So it returns to the
beginning of the outer loop, sets m to 2, and starts the next iteration.
During this second iteration of the outside loop, the inner loop will
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 Spring '10
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