I plan to use VML to evalaute the following functions:
y = x / (exp(x) - 1) and dy/dx = 1/(exp(x)-1) - x exp(x)/(exp(x)-1)^2
I have to make sure that, i do not get NAN or Infinity at x =0 or x << 1
Any suggestions on how to write the subroutine.
for y i use, expm1 and code works fine i.e, limit x->0 y = 1
using expm1 in dy/dx i am getting, infinity for small x say 1D-20.
In case of rare small arguments we suggest using VML callback feature to catch INF or NaN results and rewrite them by any required values.
Currently we are thinkng about mathematical solution for this issue - still in process.