2,                   dxz
4,4,4,4,             xmin_xtend,xmax_xtend,zmin_xtend,zmax_xtend
0,0.300,             tmin,tmax
0,                   mu0
5,5,0,0,             mu1_h,mu1_v,mu1_d,theta1
0,0,0,0,0,           mu2_h,mu2_v,mu2_d,theta2,mu2_m
0,0,1,               xwidth,zwidth,cwait
1,                   iop_vin
0,0,3000,5,45,       xo_in,zo_in,vo_in,a_in,phi_in
1,                   iop_vref
0,0,2500,0,0,        xo_ref,zo_ref,vo_ref,a_ref,phi_ref
0,0,0,0,             iop_topo,z_topo,v_reduce,airspeed
2,                   iop_tout
0.000050,0.100,      errlim,tcutoff
10,25,               niter,itmax

Notes:
  1. dxz: Spatial grid interval (positive).
  2. xmin_xtend, xmax_xtend, zmin_xtend, zmax_xtend: Extension distances for slowness model edges (non-negative).
  3. tmin, tmax: Minimum and maximum observed traveltimes to use in inversion (non-negative).
  4. mu0: `Zeroth derivative' constraint weight (non-negative, 0=no regularization).
  5. mu1_h, mu1_v, mu1_d, theta1: Parameters defining first derivative constraints:
    mu1_h: horizontal derivative weight (non-negative, 0=no regularization).
    mu1_v: vertical derivative weight (non-negative, 0=no regularization).
    mu1_d: directional derivative weight (non-negative, 0=no regularization).
    theta1: angle of directional derivative (degrees, rel to horizontal).
  6. mu2_h, mu2_v, mu2_d, theta2, mu2_m: Parameters defining second derivative constraints:
    mu2_h: horizontal derivative weight (non-negative, 0=no regularization).
    mu2_v: vertical derivative weight (non-negative, 0=no regularization).
    mu2_d: directional derivative weight (non-negative, 0=no regularization).
    theta1: angle of directional derivative (degrees, rel to horizontal).
    mu2_m: mixed derivative weight (non-negative, 0=no regularization).
  7. xwidth, zwidth: Horizontal and vertical dimensions of rectangular smoothing filter (0=no filter in coorinate direction). These values are in model distance units (e.g. meters), not in number of grids!
    cwait: Center weight of 'tent-shaped' distribution of filter weights (1.0=uniform weighting).
  8. iop_vin: Initial velocity model option flag (1=linear velocity formula, 2=read from external file).
  9. xo_in, zo_in, vo_in, a_in, phi_in: Linear velocity parameters for initial velocity model:
    xo_in, zo_in: Horizontal and vertical coordinates of reference point.
    vo_in: Velocity at reference point.
    a_in: Magnitude of velocity gradient.
    phi_in: Direction angle of velocity gradient (degrees, rel to horizontal).
  10. iop_vref: Reference velocity model option flag (0=initial model, 1=linear velocity formula, 2=read from external file).
  11. xo_ref, zo_ref, vo_ref, a_ref, phi_ref: Linear velocity parameters for reference velocity model:
    xo_ref, zo_ref: Horizontal and vertical coordinates of reference point.
    vo_ref: Velocity at reference point.
    a_ref: Magnitude of velocity gradient.
    phi_ref: Direction angle of velocity gradient (degrees, rel to horizontal).
  12. iop_topo: Topography option flag (0=ignore, 1=horizontal surface, 2=read surface topography from external file).
    z_topo: z-coordinate of a horizontal plane surface (for iop_topo=1).
    v_reduce: Velocity reduction factor above topographic surface (greater than 1.0).
    airspeed: Speed of sound in air.
  13. iop_tout: Traveltime output option flag (0=none, 1=predicted traveltimes, 2=final traveltime resiudals).
  14. errlim, tcutoff: Parameters defining treatment of traveltime residuals:
    errlim: Rms error limit for terminating tomographic iterations (non-negative).
    tcutoff: Upper limit for including residuals in inversion (positive).
  15. niter, itmax: Iteration parameters:
    niter: Maximum number of tomographic iterations (positive integer).
    itmax: Number of LSQR iterations (positive integer).

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