log

Logarithm by tau approximation for rtau object.


Syntax
   f = log(r)

Description
   F = log(r) is a function to approximate by tau method log(r), r in 
   [a, b]. We are using schursolver function, which will decide the 
   approximation degree to achieve 1e-16.

Input
   r = rigth member in tau method (rtau object).

Output
   f = coefficients of log(r).

See also
  sin, sinh, cos, cosh and exp.