x=sqrt(a^2*(1-y^2/b^2));     r=ceil(3+2*y);     x=ceil(x);     if r==1         I(m/2,m/2+x)=155+100*y;       elseif r==2         I(m/2:1:m/2+1,m/2+x:1:m/2+1+x)=155+100*y;       elseif r==3         I(m/2-1:1:m/2+1,m/2+x)=155+100*y;         I(m/2,m/2-1+x:1:m/2+1+x)=155+100*y;     elseif r==4         I(m/2-1:1:m/2+1,m/2-1+x:1:m/2+1+x)=155+100*y;     elseif r==5         I(m/2-1:1:m/2+1,m/2-1+x:1:m/2+1+x)=155+100*y;         I(m/2-2:1:m/2+2,m/2+x)=155+100*y;         I(m/2,m/2-2+x:1:m/2+2+x)=155+100*y;     end