Readme for VzEST -  dV/dz estimation for migration velocity analysis.

Note:
A conjugate gradient algorithm is used to solve a linear system of
equations for the velocity and the vertical velocity gradient.

Reference:
 This program is design for postmigration velocity analysis.  It is
 bsed on Zhaobo Meng's thesis, chapter 4.  

 "Tetrahedral based earth models, ray tracing in tetrahedral models
 and analytical migration velocity analysis", Ph. D. thesis,
 Center for Wave Phenomena, Department of Mathematical and Computer
 Sciences, Colorado School of Mines. Jan. 1999. 

 vzest converts the traveltime misfits (offset??.picks)
 to depth misfits, by multiplying the velocity at the base horizon.  

 For vzest, not all CIGs are used (because there may not be enough data.
 Only those CIGs from nxrtbeg to nxrtend and from nyrtbeg to nyrtend are
 used for velocity and depth update.  Similarly, not all offsets are used, 
 user can specify how many offsets to use and what offsets to use.  They 
 are specified by isort(1), isort(2),..., isort(npicks).

Instructions for using vzest are contained at the top of the source code:
vzestf.f.


John Stockwell	 | jstockwe@mines.edu
Center for Wave Phenomena (The Home of Seismic Un*x)
Colorado School of Mines
Golden, CO 80401 | http://www.cwp.mines.edu/cwpcodes
voice: (303) 273-3049  |    fax: (303) 273-3478.
