A lot of time i finded but i have a dubt about this why this is happen each time number of equation for finding parameter a_12 is 4 but this time is 28 which i thoght some thing must be mistake also the author of paper use u=2(ln(f))_xx which is wronge and not satisfy but i try to find R which is strange again is not number contain parameter but is satisfy also in equation 14 i don't know each i is 2 or 1 or it can be i remain itself?
thanks for any help ?