Matlab Tutorial : For Loop

For loop's syntax looks like this:

for loop_index = vector
    code;
end

This will iterate each element of the vector.

Let's write our first for loop:

for i = 1:3
    i
end

The code will print out 1, 2 and 3.

Next try another one:

v = -3:3;
for i = 1:length(v)
    v(i)
end

If we run the code, we get -3, -2, ..., 2, 3

The following code will add up each element of a vector, and display the result after ending the for loop:

v = 1:10;
sum = 0;
for i = 1:length(v)
    sum = sum + v(i);
end
disp(sum)

We can specify the step size of the loop:

for loop_index = start: step_size : end
    code;
end

Suppose We want to add only odd numbers from the numbers in 1:10

sum = 0;
for i = 1:2:10
    sum = sum + i;
end
disp(sum)    % 25

The vector for the loop index does not have to be in order:

a = 1:10;
indx = [1 9 2 4];
sum_a = 0;
for i = indx
    sum_a = sum_a + a(i);
end
disp(sum_a)  % 16

The loop will access the elements of vector a starting from the 1st, 9th, 2nd and 4th.

a = 1:10;
v = zeros(1,length(a));
sum_a = 0;
for i = 1:length(a)
    sum_a = sum_a + i;
    v(i) = sum_a;
end
figure;
plot(v);

We can also check the result from the Variable window by double clicking the v on Workspace pane:

Sometime we want to have several lines be commented out or uncomment those lines. We have short-keys:

1. Select the text
2. Use Ctrl-R to comment
3. Use Ctrl-T to uncomment