How to make coodinates bounce off the screen edge

Hey all, Having some issues with the loops in my code, so the aim is to continuously bounce a set of coordinates off the edge of the screen up until a certain time. The coordinates change, however, once they reach a limit they just stay there and I can't get them to reverse. I've tried a few variations in my code but any feedback would be welcome.

xCoord = randi([20,30],1,1); yCoord = randi([20,30],1,1);

speed_1 = 1;

boundsLeft = 0; boundsTop = 0; boundsRight = 100; boundsBottom = 90;

Coords_1 = [xCoord, yCoord]

timeID = tic;

while 1

    Coords_1 = Coords_1 + speed_1

    if (toc(timeID) > 0.1)
        break;
    end

    if Coords_1 > boundsRight
        Coords_1 = Coords_1 - speed_1;
    elseif Coords_1 > boundsBottom
        Coords_1 = Coords_1 - speed_1;
    end

    if Coords_1 < boundsLeft
        Coords_1 = Coords_1 + speed_1;
    elseif Coords_1 < boundsTop
        Coords_1 = Coords_1 + speed_1;
    end

end

Answer 1

[Thorsten]

You have to make the following changes to your code

1. test x and y coordinates separately using Coords_1(1) and Coords_1(2)
2. reverse the direction after the bounds have been reached by using speed_1 = - speed_1;
3. use - speed_1 also for the left and bottom border, to undo the + speed_1 above

And it would be better to rename speed_1 to dxy. I also added a plot to check the results and increased the time:

xCoord = randi([20,30],1,1); yCoord = randi([20,30],1,1);

speed_1 = 1;

boundsLeft = 0; boundsTop = 0; boundsRight = 100; boundsBottom = 90;

Coords_1 = [xCoord, yCoord]

timeID = tic;
axis([0 100 0 100])
hold on
while 1

      Coords_1 = Coords_1 + speed_1
      if (toc(timeID) > 10)
          break;
      end
      if Coords_1(1) > boundsRight
          Coords_1(1) = Coords_1(1) - speed_1;
          speed_1 = -speed_1;
      elseif Coords_1(2) > boundsBottom
          Coords_1(2) = Coords_1(2) - speed_1;
           speed_1 = -speed_1;
      end
      if Coords_1(1) < boundsLeft
          Coords_1(1) = Coords_1(1) - speed_1;
           speed_1 = -speed_1;
      elseif Coords_1(2) < boundsTop
          Coords_1(2) = Coords_1(2) - speed_1;
           speed_1 = -speed_1;
      end
      plot(Coords_1(:,1), Coords_1(:,2), 'o')
      drawnow

end

[gurmukh panesar]

Thank you!