the loop does not display results

Hello! There is a matrix and I need to find the first value less than 90

clear all 
close all
X=[ 80 90 100 110 100 95 90 20
     80 90 100 150 100 95 90 20
    80 90 100 150 100 95 90 20
    80 90 100 150 100 95 90 20
     80 90 100 150 100 95 90 20
      80 90 100 150 100 95 90 20
       80 90 100 150 100 95 90 20
   80 90 100 150 100 95 90 20
    80 90 100 150 100 95 90 20]' ;
[~,loc]=max(X); % search j
i=1:length(X(:,1)); % search i
j=loc; 
while X(i,j)>90 
    jx(i)=j(i)+1 % find out how many j are running in iteration 1
end
 

jx is not shown at all, although the condition is true

while X(i,j)<90 
    jy(i)=j(i)-1 
end

first cycle find out the quantity j while condition X> 90 at each iteration

second cycle find out the quantity j while condition X <90 at each iteration

and the problem I do not see jx and jy

[Adam]

i and j are vectors so

while X(i,j)

will not do what you want. You can either loop around all the values testing the condition on each or you can use a vectorised approach.

    X(i,j) < 90

returns a logical 8x9 array with a 1 (true) in the places that fulfil the condition and 0 otherwise. I'm not really sure what you want jy to output though since as it currently is it doesn't make sense as j is a row vector and i an 8x9 array.

[Lev Mihailov]

I do not understand,

% for the first iteration 
while X(i,j)>90  % X(1,4) [110 100 95 90 20]
    jx(i)=j(i)+1 % here I do not know what to do 
    % %  jx(1)=j(1)+1 % but I need to do while the whole condition is satisfied
    % [110 100 95 90 20] % 
    %  jx(1)=j(1)+1 
    %  jx(1)=j(1)+1  this condition for the first iteration must be met twice
end

Answer 1

[Philippe Lebel]

You are not looping over the values of "i" nor "j"

i=1:length(X(:,1))

i =

     1     2     3     4     5     6     7     8
j =

     4     4     4     4     4     4     4     4     4
     

If you try to evaluate X(i,j), it is equivalent to say that you try to evaluate X([1 2 3 4 5 6 7 8], [4 4 4 4 4 4 4 4 4])

If you want to do what i think you want to do, here is the code:

clear all 
close all
X=[ 80 90 100 110 100 95 90 20
     80 90 100 150 100 95 90 20
    80 90 100 150 100 95 90 20
    80 90 100 150 100 95 90 20
     80 90 100 150 100 95 90 20
      80 90 100 150 100 95 90 20
       80 90 100 150 100 95 90 20
   80 90 100 150 100 95 90 20
    80 90 100 150 100 95 90 20]' ;
[~,loc]=max(X); % search j
j=loc; 
for i = 1:length(X(:,1))
    for k = 1:length(j)
        jx(i)=j(i)+1 % find out how many j are running in iteration 1
        if X(i,j(k))>90
            break
        end
    end
    if X(i,j(k))>90
        break
    end
end

this is not optimal but it is easier to understand (i think)

[Lev Mihailov]

I like this code, but why does it count jx only 3 times ?

jx =

     5     5     5

[Philippe Lebel]

this is not relevant to the question asked in this post.

I don't know what is the intent behind your code so i don't know how to respond to this.

[Lev Mihailov]

code goal get jx per column.

And the next question is, can a matlab work with its iterations?