NAME
    magafd - Define magnetization and ambient magnetic field direction
    mpoint - Specify point source and its parameter
    mvline - Specify vertical line source and its parameter
    mhrect - Specify horizontal rectangle surface source and its parameter
    mprism - Specify rectangular block source and its parameter
    calma  - Calculate magnetic anomaly at specified observation point

 (Note)  Assume righthanded Cartesian coordinates X pointing North, Y pointing
       East, and Z pointing Down.  All units of lengths can be arbitrary as far
       as they are common to all lengths.

SYNOPSIS

      call magafd(am, the, phi, dip, dec)
  am        [float]  Magnetization intensity (in A/m)
  the, phi  [float]  Inclination and declination (in degrees) of magnetization
  dip, dec  [float]  Inclination and declination (in degrees) of ambient field
                      (Earth's magnetic field)

      call mpoint(xc, yc, zc, vol)
      call mvline(xc, yc, zs, w, area)
      call mhrect(xs, xt, ys, yt, zc, h)
      call mprism(xs, xt, ys, yt, zs, w)
  xc, yc    [float]  Horizontal coordinates of source center
  zc        [float]  Downward coordinate of source center
  xs, xt    [float]  X-axis range (lower and upper limits) of source
  ys, yt    [float]  Y-axis range (lower and upper limits) of source
  zs, w     [float]  Top deapth and thickness in depth range
                     If w=0., bottom unlimitted model is assumed.
  vol       [float]  Volume represented by a point
                      (in the unit of cube of common length unit)
  area      [float]  Area of cross-section represented by a line
                      (in the unit of square of common length unit)
  h         [float]  Thickness of the body represented by a surface
                      (in the unit common with lengths)

      f = calma(xp, yp, zp)
  xp, yp    [float]  Horizontal coordinates of the point of calculation
  zp        [float]  Depth coordinate of the point of calculation
  f         [float]  Calculated result.
                     Total force (in nT) value of magnetic anomaly is given.