this function calculates the delay caused by the earth's
ionosphere for the one way transit of a signal.  the answer is
returned in sec.  the dummy variables in the order in which
they appear are;
1. theta - the zenith angle of the source in radians
2. dmx - the peak electron density in electrons /c.c.
3. amx - the altitude above the surface of the earth of
the peak density in km.  if it is negative, a value of 350 km.
is used
4. freq - the frequency of the source signal in hz
5. flag - if flag is less than 0.0, the calculation is for
the phase delay, otherwise the group delay is calculated
if theta is less than 0 or greater than pie, theta is
assumed to be 0.