Do you have the coordinates of the point and the center (in standard Cartesian coordinates)? If so, just use norm and atan2 of the difference between the two:
p1 = rand(2,1)
p2 = rand(2,1)
d = p2 - p1
norm(d)
atan2(d(2),d(1))
EDIT TO ADD (In response to your comment): Still the same idea -- atan(delta_y,delta_x). It seems that you have data in the form of whole vectors of (x,y) points, and a single center point, in which case:
% coordinates of points
X = [1;2;3;4];
Y = [9;8;7;6];
% coordinates of center
X0 = 2;
Y0 = 2;
% take the difference
dX = X - X0;
dY = Y - Y0;
% and calculate the length
sqrt(dX.^2 + dY.^2)
% and angle
atan2(dY,dX)
% or atan2d(dY,dX) if you prefer degrees to radians
% visualize, for sanity
plot(X,Y,'o',X0,Y0,'x')
