problem with if statement

Hi Guys,

This is a very basic question. I want to figure out which quadrant a point lies in from the value I get from atan2. I dont know if there is a simpler way but I wrote a code containing a series of if statements and it isnt executing right. Can anyone tell me what is wrong in it. Your help is greatly appreciated.

    if 0<ang<1.5708
        quad=1;
    end
    if 1.5708<ang<3.1416
        quad=2;
    end
    if -1.5708<ang<0
        quad=3;
    end
    if -3.1416<ang<-1.5708
        quad=4;
    end

Thanks, NS

[sco1]

I'll look at it in a second, but I would suggest using pi() instead of discrete numbers in order to avoid errors where your point lies on one of the axes.

Answer 1

[Wayne King]

if (0<ang && ang <1.5708)
        quad=1;
    elseif (1.5708<ang && ang<3.1416)
        quad=2;
    elseif (-1.5708<ang && ang<0)
        quad=3;
    else 
        quad=4;
    end

You can't do 0<ang<pi/2

[NS]

Thanks. Works nicely.

Answer 2

[Fangjun Jiang]

What is wrong is that "0<ang<1.5708" is not a valid statement according MATLAB M-language syntax. You will need to use

and(0<ang, ang<1.5708)

Or

0<ang && ang<1.5708

[NS]

Oh I didnt know that. Thanks I will change my code :)

Answer 3

[sco1]

I don't think MATLAB will handle the logic statements when put that way, try using an and statement instead: I would also suggest using elseif just because it makes things look neater.

For example:

if ang > a && ang < b
quad = x
elseif ang > b && ang < c
quad = y

etc.

edit: I'm a slow typer!

[NS]

Thanks Sam. :)