@Preben Alsholm 

Dear "Preben Alsholm" ; I applied your presented code and i found that helpful. But i have a general problem. When i run this code to obtain Figure4, in page 16 of the paper http://arxiv.org/abs/gr-qc/0612180 it gives a diagram similar to lower half of the Figure4. It do not plot upper section of Figure4. What do i shoud consider to obtain the complete diagram?

Othe problems is: In the line "varchange:=[x(t),z(t),w(t)]=~(pvar/~(1-P))" how do you transform X_i coordinates to p-coordinates? i mean from, for instance p3=w/(1+d), to w=p3/(1-d)? where does the mines signature come from?

thanks for your helps