26.16.2  Cross ratio of four collinear points

The cross ratio of four numbers a,b,c,d is [(c−a)/(c−b)]/[(d−a)/(d−b)].

The cross_ratio command finds the cross ratio.

• cross_ratio takes four arguments: a,b,c,d, complex numbers.
• cross_ratio(a,b,c,d) returns the cross ratio, [(c−a)/(c−b)]/[(d−a)/(d−b)].

Examples