  sn(w+iK')=1/(k sn w)             max error 1.38e-40
  cn(w+iK')=-i dn/(k sn)           max error 1.45e-40
  sn(w+K+iK')=dn/(k cn)            max error 1.66e-40
  cn(w+K+iK')=-ik'/(k cn)          max error 1.54e-40
  dn(w+K+iK')=ik' sn/cn            max error 1.15e-40
  sn(w+2iK')=sn                    max error 1.08e-39
  cn(w+2iK')=-cn                   max error 1.08e-39
  sn,cn(w+2K)=-sn,-cn              max error 2.98e-39
  dn(w+2K)=dn, dn(w+4iK')=dn       max error 3.14e-39
  res dn at iK' = -i               max error 1.36e-26
