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From: Jakob on 25 Apr 2010 15:17
Hello,
My group and I are dealing with MATLAB for the first time and we are analyzing a wind turbine..
We want to see what forces act on the wind turbine during a rotation.


-----
intv=2*pi/64
for theta=0:intv:2*pi

if 0<=theta<pi/2
alpha = 1
elseif pi/2<=theta<pi
alpha = 2
elseif pi<=theta<3/2*pi
alpha = 3
else
alpha = 4
end

alpha
end
------

When I run this, I only get alpha = 1.. We have functions instead of "1", "2", "3" and "4".. But I hope you get the point :)

Greetings Jakob
From: Tim Love on 25 Apr 2010 15:48
"Jakob " <jhaerv.remove_this.09(a)student.aau.dk> writes:

>if 0<=theta<pi/2
This doesn't do what mathematicians expect. Try

if 0<=theta && theta<pi/2

From: Matt Dunham on 25 Apr 2010 16:04
"Jakob " <jhaerv.remove_this.09(a)student.aau.dk> wrote in message <hr24fh$7uk$1(a)fred.mathworks.com>...
> Hello,
> My group and I are dealing with MATLAB for the first time and we are analyzing a wind turbine..
> We want to see what forces act on the wind turbine during a rotation.
>
>
> -----
> intv=2*pi/64
> for theta=0:intv:2*pi
>
> if 0<=theta<pi/2
> alpha = 1
> elseif pi/2<=theta<pi
> alpha = 2
> elseif pi<=theta<3/2*pi
> alpha = 3
> else
> alpha = 4
> end
>
> alpha
> end
> ------
>
> When I run this, I only get alpha = 1.. We have functions instead of "1", "2", "3" and "4".. But I hope you get the point :)
>
> Greetings Jakob

Here's what's happening:

if 0<=theta<pi/2

Matlab evaluates 0<=theta first, suppose this is true. Matlab then evaluates
true < pi/2, and since the right hand side evaluates as a double, true is converted
to the double 1, hence 1 < pi/2 is evaluated which will return false.
In fact this expression will always return false regardless of the value of theta.

What you need is this:

if (0 <= theta) && (theta < pi/2)
From: Jakob on 25 Apr 2010 16:35
Thanks a lot to both of you!
I got excatly what I needed..
I'm glad you know what I mean, when MATLAB doesn't. Thanks again :)


"Matt Dunham" <mattdunham(a)yahoo.com> wrote in message <hr277l$2t1$1(a)fred.mathworks.com>...
> "Jakob " <jhaerv.remove_this.09(a)student.aau.dk> wrote in message <hr24fh$7uk$1(a)fred.mathworks.com>...
> > Hello,
> > My group and I are dealing with MATLAB for the first time and we are analyzing a wind turbine..
> > We want to see what forces act on the wind turbine during a rotation.
> >
> >
> > -----
> > intv=2*pi/64
> > for theta=0:intv:2*pi
> >
> > if 0<=theta<pi/2
> > alpha = 1
> > elseif pi/2<=theta<pi
> > alpha = 2
> > elseif pi<=theta<3/2*pi
> > alpha = 3
> > else
> > alpha = 4
> > end
> >
> > alpha
> > end
> > ------
> >
> > When I run this, I only get alpha = 1.. We have functions instead of "1", "2", "3" and "4".. But I hope you get the point :)
> >
> > Greetings Jakob
>
> Here's what's happening:
>
> if 0<=theta<pi/2
>
> Matlab evaluates 0<=theta first, suppose this is true. Matlab then evaluates
> true < pi/2, and since the right hand side evaluates as a double, true is converted
> to the double 1, hence 1 < pi/2 is evaluated which will return false.
> In fact this expression will always return false regardless of the value of theta.
>
> What you need is this:
>
> if (0 <= theta) && (theta < pi/2)
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