Path: news.mathworks.com!not-for-mail From: "Natalie Sin Hwee " <sin.ng09@imperial.ac.uk> Newsgroups: comp.soft-sys.matlab Subject: Re: finding distances that satisfy the equation ? (confused :'( , please help) Date: Mon, 29 Mar 2010 09:56:04 +0000 (UTC) Organization: Imperial College Lines: 30 Message-ID: <hoptfk$7du$1@fred.mathworks.com> References: <hoo666$8u3$1@fred.mathworks.com> <hoo9it$r4p$1@fred.mathworks.com> Reply-To: "Natalie Sin Hwee " <sin.ng09@imperial.ac.uk> NNTP-Posting-Host: webapp-05-blr.mathworks.com Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Trace: fred.mathworks.com 1269856564 7614 172.30.248.35 (29 Mar 2010 09:56:05 GMT) X-Complaints-To: news@mathworks.com NNTP-Posting-Date: Mon, 29 Mar 2010 09:56:04 +0000 (UTC) X-Newsreader: MATLAB Central Newsreader 2069448 Xref: news.mathworks.com comp.soft-sys.matlab:621415 "Roger Stafford" <ellieandrogerxyzzy@mindspring.com.invalid> wrote in message <hoo9it$r4p$1@fred.mathworks.com>... > "Natalie Sin Hwee " <sin.ng09@imperial.ac.uk> wrote in message <hoo666$8u3$1@fred.mathworks.com>... > > ........ > > for node=1:a; > > for u=1:a; > > theta(node,u)=atan2(imag((x(1,u)-x(1,node))+[(y(1,u)-y(1,node))*i]),... > > real((x(1,u)-x(1,node))+[(y(1,u)-y(1,node))*i])); > > end > > end > > > > [thetasort,R]=sort(theta,1); % increasing angles downward (column) > > > > sect1=((0<thetasort) & (thetasort<(0.25*pi))); > ---------- > This looks like a very awkward way to compute your angles. Why take the trouble to create complex-valued quantities only to convert them back to real values again? Why not just say this: > > theta(node,u)=atan2(y(u)-y(node),x(u)-x(node)); > > With either method you will be obtaining angles measured counterclockwise from the x-axis to the directed line between each pair of points and which range from -pi to +pi. You will be selecting only those between 0 and +pi/4, and in particular rejecting those between -pi/4 and 0. In the cases where node equals u along the diagonal your results will be meaningless. Is this what you want? > > Why do you sort the angles before subjecting them to your range tests? What you will get is a series of falses, then trues, and finally falses. As your code stands there is no way to associate this with the original data in x and y. > > Roger Stafford hiya, basically i used a more 'complex' method because im working from 0-pi and 0 - (-pi) hence the atan2. im nore sure why im using the real and imaginary. apparently it will work in 3d (through my previous quetisons on the forum) - which i will later need to make my model into 3d !! ^^ thanks natalie