function [boo] = two_black_holes(i)

xx = (1+0.*i')*i;
yy = i'*(i.*0+1);

r1sq = (xx+1).^2 + yy.^2;
r2sq = (xx-1).^2 + yy.^2;

boo = r1sq.^(-1/2) + r2sq.^(-1/2);
