Applying a for loop to every column in a vector

I have some code which tells me the largest value in the first column of a matrix, as well as the index (row) at which it occurs. First, I have noticed these two functions work properly, except when the largest value appears in the first row, causing the outputed index to be incorrect, why might this be? Next, I need to perform this operation (finding the largest value in each column) across each column in the matrix, how can this be done with a loop of some sort? my current code is below

x = randi (10,7,4)
[rows, columns] =size (x);
max = x(1,1);
for i = 1:rows %need to apply this 'for' loop on all columns of x and output a vector of all the results
    if x(i,1)>max;
        max =x(i,1);
        index =i;%index output is incorrect when max is in first row
    end
end
index
max

[KSSV]

Dont use variable name a function name. Rename max with something else.

Answer 1

[J. Alex Lee]

Agree with KSSV, avoid naming as "max", but in this case it is not causing your problem.

Your problem is that "index" should not be defined in case the max value is in the first row, because you would never execute the assignment

index = i

Assuming you've run several times without clearing variables, you should have noticed that the incorrect index is in fact the index from the previous time you ran.

[J. Alex Lee]

By the way, if your purpose is to actually find the max value and index, and not just to learn about coding, then just do

x = randi (10,7,4)
[maxval,maxidx] = max(x(:,1))

But on the other hand, what do you expect to happen if you had duplicate values in the first column, which are the largest value, e.g.,

x =

     3     5     1     3
    10     2     4     2
     2    10     3     2
     9     1     9     9
     6     8     5     6
    10     9    10     6
     1     9     2     2

[Louis Meyer]

Great, I was able to get around the index problem so it now works properly. Now my only issue is how to apply that operation to every column, such that the output is two vectors, one of the maximum value in each column, and one of the row number (index) in which the maximum value appears in each column. Essentially I need to write my own code to mimick the build in max function. Thanks for your help so far!

[J. Alex Lee]

you can "nest" loops. instead of (i,1), think about if you could do (i,j) where j was another index for another loop either inside or outside of your current loop over i.