Need Help to find the error

2012 10 21
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Hello, I need from an array consisting of 10,000 items and are the coordinates (X and Y) of the ellipse to determine the minimum and maximum distance between two points. The problem is that the origin of 10000 should have 9999 range, the mine, the program calculates only 9998. you can verify using the command size(dist).
clear all
clc
A=[2/3 -2/3; 2/3 7/3];
[eigenvektor, eigenvalue]=eig(A);
n = 10000;
theta = linspace(0,2*pi,n);
r = 1;
x =r.*cos(theta);
y =r.*sin(theta);
plot(x,y,'.')
v = [x;y];
w=A*v;
xcoor=w(1,:);
ycoor=w(2,:);
i=0;
while i<n
i=i+1;
dxx2=xcoor(n-i:length(xcoor)-i);
dxx1=xcoor(n-(i+1):length(xcoor)-(i+1));
dyy2=xcoor(n-i:length(ycoor)-i);
dyy1=xcoor(n-(i+1):length(ycoor)-(i+1));
dist(i)=sqrt( (dxx2-dxx1)^2 + (dyy2-dyy1)^2);
end

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Azzi Abdelmalek
Azzi Abdelmalek 2012-10-21
which distance do you want, maybe there is a better way to do it
Alex
Alex 2012-10-21
distance between two points of the ellipse. The circumference of an ellipse has 10 000 points. maxdistance=max(dist) maxdistance =0.0008378
mindistance=min(dist) mindistance = 6.581D-08 The formula for the distance set me right. The problem is that in its cycle, I do not get to a end of the array.

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Azzi Abdelmalek
Azzi Abdelmalek 2012-10-21
编辑：Azzi Abdelmalek 2012-10-21

1 个投票

r = 1;
x =r.*cos(theta);
y =r.*sin(theta);
plot(x,y,'.')
v = [x;y];
w=A*v;
xcoor=w(1,:);
ycoor=w(2,:);
figure,plot(xcoor,ycoor)
dist=sqrt(xcoor.^2+ycoor.^2)*2
min(dist)
max(dist)
If the origin of your ellipse is not (0,0) we can make translation
Also you don't need 10000 points, 5000 points are enough
dist=sqrt(xcoor(1:5000).^2+ycoor(1:5000).^2)

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Alex
Alex 2012-10-21
Not sure that is correct ... As I understand it from the task to determine the distance between two adjacent points in the plane of the ellipse, rather than minimum and maximum distance between any two points in the plane of the ellipse. "The set of vectors w contains vectors with maximal and minimal length (Euclidean norm). Compute these two values" or am I wrong again?
Azzi Abdelmalek
Azzi Abdelmalek 2012-10-21
编辑：Azzi Abdelmalek 2012-10-21
do you want the distance between two consecutive points?
then look at Star's answer
Alex
Alex 2012-10-21
thank you very much:)

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更多回答（1 个）

Star Strider
Star Strider 2012-10-21

0 个投票

Instead of your while loop, I suggest:
dxx = diff(xcoor);
dyy = diff(ycoor);
dist = hypot( dxx, dyy);
Does this do what you want?

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