Relationship between (i & j) of a nested for loop and (x & y) coordinates?

If I have a nested for loop:

T=ones(n)
for i = 1 : nx
    for j = 1 : ny
    T(i,j) = %something
    end
end

I understand i goes down and j goes right in a loop but isn't it supposed to be the opposite where i is the horizontal row nd j is the vertical column?

for i = 1 : nx
    for j = 1 : ny

Does this mean that the T(i,j) I'm plotting is in the direction of:

I'm a little confused about (i&j) and (x&y)..

Answer 1

[KSSV]

It moves from bottom to top and left to right. Check with below:

nx = 10 ;
ny = 10 ;
figure
hold on
for i = 1:nx
    for j = 1:ny
        plot(i,j,'*')
        drawnow
        text(i,j,num2str([i j]))
    end
end

Why you are confused with direction? How does it matter?

[Amanda Liu]

Hmm..because if I were to assign boundary conditions at the sides of a square (left right top bottom)

should i code like this

T(:,1) = 2 % Left
T(:,end) = 3 % Right
T(1,:) = 1 % Top
T(end,:) = 4 % Bottom

or

T(:,1) = 4 % Left
T(:,end) = 1 % Right
T(1,:) = 2 % Top
T(end,:) = 3 % Bottom

but i do noticed that the top and bot should be reversed so that it plots in the correct direction

T(1,:) % Should be Bottom value
T(:,end) % Should be Top value

Answer 2

[Dhruv G]

As @KSSV has noted, the for loop just means that the indices will increase while the loop runs. In a table, what you've drawn is correct. But in a right-handed coordinate plane ( the normal axes that we're used to), the indices increase when moving right and moving upward. The indices of the for loop will obey this

[Amanda Liu]

Okay, thank you.