The average FTCE for material vectors that start from region 1 and end up in region 2, calculated for total time T and averaged over such material vectors whose number is [N.sub.12], is
[N.sub.0] vectors that spend all the time in region 2, we obtain the average FTCE for the length of a material vector:
To obtain the FTLE for its shorter semiaxis, [[lambda].sub.2], we first find the FTCE for its area, [[lambda].sub.A].