Using logical AND in an if statement?

Hi, so I'm working on a problem and have an if statement nested in a for-loop. Basically I can put

if x >= -12
      plot(x)
 end

and my program will work, but when I add the second statement

    if x >= -12 & x < -3
        plot(x)
    end

Nothing happens at all. I can put the statement

     x >= -12 & x < -3

in the console it will give me the values, but I just don't understand why it isn't functioning properly in my if-statement.

Here's the relevant code:

    for i = -12 : .5 : 12
        x = [-12: .5: 12];
        if x >= -12 & x < -3
            plot(x)
        else
            fprintf('error ');
        end   
    end

Also if someone could point me in the right direction on using my for-loop index instead creating variable x with the same values that would be great. Just not too sure on how to make it save each value in a matrix.

Using R2015a

EDIT: It seems that evaluations when x < -3 is causing the issue. I still don't know why. I've tried maxing x > -3, x >=-3, and x <= -3 and I still am not getting any output except for my error message.

Answer 1

[Kelly Kearney]

When evaluated on a vector, conditional statements return true only if all elements of the vector match the condition. So

x = [-12: .5: 12];
if x >= -12 & x < -3
  % do something
end

is the same as

x = [-12: .5: 12];
if all(x >= -12 & x < -3)
  % do something
end

And in your case, that statement evaluates as false, so nothing happens.

Logical indexing is the better way to achieve what you want:

x = [-12: .5: 12];
plot(x(x > -12 & x <-3));

or if you want to stick with a for loop and plot each point as a different object (not really recommended, but just for reference), you'll need to index:

 hold on;
 x = [12:0.5:12];
 for ii = 1:length(x)
   if x(ii) > -12 && x(ii) < -3
     plot(x(ii));
   end
 end