charge simulation method

how can I choose points from the surface of a circle? how can I subtract each element of a matrix from the other elements of the same matrix?

[ahmed]

help me plzzzzzz

[Fangjun Jiang]

You need to clarify your question. What is the surface of a circle? For the second part, could you provide an example?

[ahmed]

1) we plot a circle and i need to choose 4 points on it

2) if i've a matrix:

f=[x1 x2 x3]

so

i wanna have:

z=[x1-x2 x1-x3 x2-x1 x2-x3 x3-x1 x3-x2]

Answer 1

[Fangjun Jiang]

f=[1 2 3];
g=bsxfun(@minus,f,f.')

The other question depends on how you plot it and how do you want to choose the point.

[ahmed]

the circle that I plot:

theta=linspace(0,2*pi,100);

xcenter=5;

ycenter=1;

radius=4;

x=xcenter+(radius*cos(theta));

y=ycenter+(radius*sin(theta));

plot (x,y,'r')

hold on

[Fangjun Jiang]

That's good! How do you want to choose the 4 points? Randomly?

[Fangjun Jiang]

N=length(x);

m=randperm(N);

m=m(1:4);

x_select=x(m);

y_select=y(m);

plot(x_select,y_select,'b*');

[ahmed]

if i have this variable

p=[p1 p2 p3;p4 p5 p6]

and i want to differential "p" to "x"

x=points on a circle

????