Two ways of iterating a vector

I have a problem with iterating a vector.

Here is part of my code (values of Best, Choices and Follower are not hardcoded ofc, I just put them not to include the entire file)

Best = 3;
Choices = [1;2];
Follower = [0;1];
for iter = 1:length(Choices)
    fprintf('i=%i\n', Choices(iter))
    fprintf('outcome=(%f, %f)\n', Best, Follower(Choices(iter)))
end
for item = Choices
    fprintf('i=%i\n', item)
    fprintf('outcome=(%f, %f)\n', Best, Follower(item))
end

When iterating by index, it works properly (result is the same as analytical solution of the problem):

i=1
outcome=(3.000000, 0.000000)
i=2
outcome=(3.000000, 1.000000)

But when I try to iterate over values, the result is:

i=1
i=2
outcome=(3.000000, 0.000000)
outcome=(1.000000, >> 

So the lines are mixed, value of Best changes? or is missing? and the last fprintf doesn't finish...

Please explain if I am doing something wrong, misunderstood sth or is it a bug?

I just noticed that the second version works properly for horizontal vectors ( eg. [1 2] instead of [1;2])...

[Stephen23]

Note that this is simple and efficient without a loop:

>> M = [1,2;3,3;0,1]
M =
   1   2
   3   3
   0   1
>> fprintf('i=%i\noutcome=(%f,%f)\n',M)
i=1
outcome=(3.000000,0.000000)
i=2
outcome=(3.000000,1.000000)

Answer 1

[Mustafa Abu-Mallouh]

In MATLAB, the for loop iterates over columns. When you define item as Choices, you're defining it as a single column. Change your loop to begin with

for item = Choices'
    fprintf('i=%i\n', item)
    fprintf('outcome=(%f, %f)\n', Best, Follower(item))
end

And it will work properly.

You could also define Choices as a row vector from the start.

See here for more information.

[Dawid Najda]

Oh right, I changed the definition to

Follower = zeros(1, hght);

and then the part that fills it accepted it, and iterating worked too.

Thanks for the explaination.