inverse loop

I want to use loop from i=180:1 and again next inserted loop j=180:1 Does matlab allow that? how I access (180,180) first rather then (0,0)...

[Amr]

sure ... use this command for i=180:-1:1 for j=180:-1:1

Answer 1

[Fangjun Jiang]

for i=180:-1:1
  for j=180:-1:1

[Scott]

thanks

Answer 2

[Jan]

Whenever you have a problem with a specific command, be sure to read the help and doc text for this command:

help for

Step S with increments of -0.1

 for S = 1.0: -0.1: 0.0, do_some_task(S), end

Answer 3

[Thomas]

Try,

    for i=180:-1:1
      for j =180:-1:1
      i
      j
      end
    end

[MH]

@Thomas is there a way in matlab where you can flip the nesting of the loops based a user's preference via a dialog box selection?

meaning if I have a dialog box that pops up when the code runs and asks, 'do you want to run the code as is or inverted' with two options 'as is' or 'inverted' and based on the selection, the code would either run as

for i=180:-1:1
    for j =180:-1:1
        i
        j
    end
end

OR

for j =180:-1:1
    for i=180:-1:1
        i
        j
    end
end

Without having a "switch" case

[John D'Errico]

@MH

Of course. You could just set the limits and the step for the loops, based on a test on the result returned from the dialog box.

for i = start:step:fin
    for j = start:step:fin
        i
        j
    end
end

Just define the values of start, step, and fin, and you are done.

[Steven Lord]

Don't try to dynamically change the code. Change the data.

x = 1:5;
if rand > 0.5
    fprintf("Flipping loop vector")
    x = flip(x);
end

Flipping loop vector

for k = x
    fprintf("Processing element %d.\n", k)
end

Processing element 5.
Processing element 4.
Processing element 3.
Processing element 2.
Processing element 1.

Depending on the random value generated when you run the code, x will be either 1:5 or 5:-1:1. The for loop will iterate over the elements in that vector. [In this case the value was greater than 0.5 so the vector got flipped, as you can see from the iterative output.]

In your case, the decision to flip or not to flip could be made based on a prompt from the user or some other computations, but the input function is not supported in answers posted on MATLAB Answers.

[Walter Roberson]

The question @MH asked is about automatically inverting the order of two loops, without having to have a switch() statement. In one case in their example the loops are nested j within i, and in the other case the loops are nested i within j.

The answer to the question is "No, there is no dialog box or editor option to automatically reverse the nesting order. You would need something like

for outer = start:step:fin
    for inner = start:step:fin
        if ReverseLoop
            i = outer; j = inner;
        else
            i = inner; j = outer;
        end
        %code
    end
end

[MH]

Thank you @Walter Roberson