Example:Draw the electric field lines for a system that consists of two charges +2q and -q for j=-1*pi:pi/12:pi y(1)=0.2*sinG): x(1)=0.2*cos0房 fori=1:400 r(①=sqrt(x(①)2+y(①2) r1(i斤sqrt(x(i^2+(3-y(0)^2): x1(①=x(①/(r(①3)+2*x(①/(rl(①^3) y1(i)y(i)/r(①3)-2*(3-yi)/c1(①^3) y(i+1)y(①)+y1(①/x1(i①)*0.01 x(i+1)x(①+0.01；Example: Draw the electric field lines for a system that consists of two charges , +2q and -q for j=-1*pi:pi/12:pi y(1)=0.2*sin(j); x(1)=0.2*cos(j); for i=1:400 r(i)=sqrt(x(i)^2+y(i)^2); r1(i)=sqrt(x(i)^2+(3-y(i))^2); x1(i)=x(i)/(r(i)^3)+2*x(i)/(r1(i)^3); y1(i)=y(i)/(r(i)^3)-2*(3-y(i))/(r1(i)^3); y(i+1)=y(i)+y1(i)/x1(i)*0.01; x(i+1)=x(i)+0.01;