fluid dynamics - Flow field around cylinder in Matlab -

i'm pretty new different plots in matlab , i'm trying write code show flow field around cylinder in matlab. i'm @ start , first of want make circle in rectangular domain (cylinder should not right in middle of field).

so far, have set want know if it's possible make cylinder more circular , less oval, because domain rectangle , not square. points on circle correct want better. tips on this? code have @ moment is:

u_i = 20;            % ambient velocity = 4;               % cylinder radius  c = -a*5;            % starting coordinate (x) b = a*10;            % ending coordinate (x) d = -60;             % starting coordinate (y) e = 60;              % ending coordinate (y)  n = a*50;            % number of intervals (step size in grid)  [x,y] = meshgrid([c:(b-c)/n:b],[d:(e-d)/n:e]');  = 1:length(x)     k = 1:length(x);         f = sqrt(x(i,k).^2 + y(i,k).^2);         if f <             x(i,k) = 0;             y(i,k) = 0;         end     end end  % definition of polar variables r = sqrt(x.^2+y.^2); theta = atan2(y,x);                                 %% creation of streamline function  z = u_i.*r.*(1-a^2./r.^2).*sin(theta);%- g*log(r)/(2*pi);  %% creation of figure  m = 100;  s = ones(1,m+1)*a; t = [0:2*pi/m:2*pi];  %% streamline plot  contour(x,y,z,50); hold on  polar(t,s,'-k'); % axis square title('stream lines'); grid off