MATLAB Language For loops Nested Loops

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Example

Loops can be nested, to preform iterated task within another iterated task. Consider the following loops:

ch = 'abc';
m = 3;
for c = ch
    for k = 1:m
        disp([c num2str(k)]) % NUM2STR converts the number stored in k to a charachter,
                             % so it can be concataneted with the letter in c
    end
end

we use 2 iterators to display all combinations of elements from abc and 1:m, which yields:

a1
a2
a3
b1
b2
b3
c1
c2
c3

We can also use nested loops to combine between tasks to be done each time, and tasks to be done once in a several iterations:

N = 10;
n = 3;
a1 = 0; % the first element in Fibonacci series
a2 = 1; % the secound element in Fibonacci series
for j = 1:N
    for k = 1:n
        an = a1 + a2; % compute the next element in Fibonacci series
        a1 = a2;      % save the previous element for the next iteration
        a2 = an;      % save ht new element for the next iteration
    end
    disp(an) % display every n'th element
end

Here we want to compute all the Fibonacci series, but to display only the nth element each time, so we get

   3
   13
   55
   233
   987
   4181
   17711
   75025
   317811
   1346269

Another thing we can do is to use the first (outer) iterator within the inner loop. Here is another example:

N = 12;
gap = [1 2 3 4 6];
for j = gap
    for k = 1:j:N
        fprintf('%d ',k) % FPRINTF prints the number k proceeding to the next the line
    end
    fprintf('\n')        % go to the next line
end

This time we use the nested loop to format the output, and brake the line only when a new gap (j) between the elements was introduced. We loop through the gap width in the outer loop and use it within the inner loop to iterate through the vector:

1 2 3 4 5 6 7 8 9 10 11 12 
1 3 5 7 9 11 
1 4 7 10 
1 5 9 
1 7 


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