@article{amos:1980:aei,
    author = {Amos, Donald E.},
     title = {Algorithm 556: {E}xponential integrals},
   journal = {ACM Trans. Math. Software},
    volume = {6},
      year = {1980},
    number = {3},
     pages = {420–428},
      issn = {0098-3500},
      note = {Single-precision Fortran, maximum accuracy 14S. For
               a Remark
              see same journal v. 9 (1983), no. 4, p. 525.},
       doi = {10.1145/355900.355913},
     links = {\URL[Remark]{http://doi.acm.org/10.1145/356056.356067},\GAMSmodule{TOMS}{556}{8595}},
     zblno = {0436.65007}}