In this case, you can try something like this.
[x,y] = meshgrid(0:0.1:1,0:0.1:1);
u = x;
v = -y;
figure
quiver(x,y,u,v)
startx = 0:0.02:1; % <=== chage the number of points in startx
starty = ones(size(startx));
streamline(x,y,u,v,startx,starty)
For the plot in your other question, you can also try to increase the number of points in the startx vector, and accordingly the number of points in starty. I am not sure why I didn't try on that question. Maybe there was some other issue. You can try it again.
