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    40.185276
  5.40    54.193501    54.193478
 12.50 23565.099609 23565.113281
 13.00 37197.699219 37197.683594
 13.50 58827.000000 58826.960938
 14.00 93193.000000 93192.507813
 14.50 147866.000000 147866.187500
 15.00 234955.000000 234955.828125