Exponential Integral Ei

    x       actual       ei(x) 
  0.10    -1.622810    -1.622813
  0.20    -0.821761    -0.821761
  0.30    -0.302669    -0.302668
  0.40     0.104768     0.104765
  0.50     0.454220     0.454220
  0.60     0.769881     0.769881
  0.70     1.064910     1.064907
  0.80     1.347400     1.347397
  0.90     1.622810     1.622812
  2.20     5.732610     5.732615
  2.40     6.600670     6.600670
  3.50    13.925400    13.925355
  3.90    18.315701    18.315716
  5.00    40.185299    40.185280
  5.40    54.193501    54.193474
 12.50 23565.099609 23565.121094
 13.00 37197.699219 37197.675781
 13.50 58827.000000 58826.957031
 14.00 93193.000000 93192.515625
 14.50 147866.000000 147866.156250
 15.00 234955.000000 234955.890625