Updates to alfdip3d.f90

The main differences between the new version and the previous
version are:

1. A parameter tdrive2 has been introduced. For idrive=4 (multiple
sine wave driving), tdrive2 gives a time scale for the decay of the
driving field.

2. A new option ppl = -1 has been introduced. When this is set, the
plasmapause density data is read from a file, 'ppmodel1.dat'. For
example, this can be used to input a density profile from
spacecraft data.

3. The roles of ixbc=2 and ixbc=3 are switched. ixbc=2 now allows
for Alfven waves to flow out of the nightside boundary of the
system, while ixbc=3 has Dirichlet boundary conditions on b3.

In addition, a number of statements that were put in for debugging purposes have been taken out.

Some new IDL routines were used, in the file 'newalfdip.pro'. The
new routines are:

eqcorrfreq: to make plots correlating the fields at two points in
the equatorial plane at a given frequency. The parameters are:
nrun: run number
var: variable used, e.g., 'bx', 'by', 'ex'
freq0: frequency for filtering
i0,i1: first and last output file to use
var0: variable on which to base the correlation
l0,lat0,mlt0: L shell, latitude and MLT for base point
itype= 1, coherence; 2, amplitude ratio; 3, cross-phase
The only relevant keyword is prfile: when set, a printed file is the data is produced

latcorrfreq: like eqcorrfreq but at a latitude other than the
equator parameters the same except for lat1,l1, which make plot at
a latitude lat1 on the field line with L-shell l1.  Note that on other field lines the values
will be for the same mu coordinate as the reference point given

latcorrfreqline: like latcorrfreq but makes a line plot.  New parametere is mlt1, the magnetic local
time for the plot

dipcorrfreq: makes correlation plots on a meridional plane.  Now mlt1 is the MLT for the plot.

Data Files for Figures in Takahashi et al. 2022:
Fig 11a: alfspeed.out: first row gives number of cells in the nu, phi, mu (i,j,k) directions
  other rows give Alfven speed in km/s, vakm(i,j,k) with i varying most rapidly
Fig 11b: enden211bz.out: as noted by column headers, first column is l-shell, second is frequency, 
  third is log of energy density in Bmu field
Fig 12: These files have the format: L-shell, MLT, Amp Ratio, Cross-phase
  Panels a,b: eqey211f20.out
  Panels c,d: eqey211f12.out
  Panels e,f: eqey211f05.out
  Panels g,h: lat10bx211f20.out
  Panels i,j: lat10bx211f12.out
  Panels k,l: lat10bx211f05.out
  Panels m,n: eqbz211f20.out
  Panels o,p: eqbz211f12.out
  Panels q,r: eqbz211f05.out
Fig 13: These files have format: L-shell, latitude, Amp Ratio, Cross-phase
  Panels a,b: dipey211f20mlt00.out
  Panels c,d: dipey211f12mlt00.out
  Panels e,f: dipey211f05mlt00.out
  Panels g,h: dipbx211f20mlt00.out
  Panels i,j: dipbx211f12mlt00.out
  Panels k,l: dipbx211f05mlt00.out
  Panels m,n: dipbz211f20mlt00.out
  Panels o,p: dipbz211f12mlt00.out
  Panels q,r: dipbz211f05mlt00.out
Fig 14: Simulation plots g-l: these are cuts through the same data set as in Figure 13.
  Panel g: dipey211f20mlt00.out
  Panel h: dipbx211f20mlt00.out
  Panel i: dipbz211f20mlt00.out
  Panel j: dipey211f12mlt00.out
  Panel k: dipbx211f12mlt00.out
  Panel l: dipbz211f12mlt00.out
Fig. 15: Simulation plots d-e: amplitude and cross-phase cut as function of MLT from dipbz211f12mlt00.out