function [t1,t2]=vint2t(vint,z,zout,tnot)
% VINT2T: compute time given interval velocity versus depth
%
% [t1,t2]=vint2t(vint,z,zout,tnot)
% [t1,t2]=vint2t(vint,z,zout);
% t1=vint2t(vint,z);
%
% Given interval velocity versus depth, compute 1 way vertical
% time as a function of depth.
%
% vint ... vector of interval velocities
% z ... vector of depths for each interval velocity.
%   Note: vint(k) is the velocity between z(k) and z(k+1). The
%   last v is used indefinitly as a half space
% zout ... vector of depths for which vertical travel times
%	are desired.
% ********* default = z ***************
% tnot ... constant time shift (seconds). (The time to z(1) )
%    Setting tnot=0 makes z(1) the reference datum
% ********** default = vint(1)/z(1) *********
%
% t1 ... vector of 1-way vertical times (seconds) corresponding to zout
% t2 ... vector of 1-way vertical times (seconds) corresponding to z
% Note: if zout was not the same as z, then you may wish to 
% compute a set of velocities to match. Use vint2vrms or vint2vave
% depending on which type of interval velocities you want.
%
% G.F. Margrave, June 1995
%
% NOTE: It is illegal for you to use this software for a purpose other
% than non-profit education or research UNLESS you are employed by a CREWES
% Project sponsor. By using this software, you are agreeing to the terms
% detailed in this software's Matlab source file.
 
% BEGIN TERMS OF USE LICENSE
%
% This SOFTWARE is maintained by the CREWES Project at the Department
% of Geology and Geophysics of the University of Calgary, Calgary,
% Alberta, Canada.  The copyright and ownership is jointly held by 
% its author (identified above) and the CREWES Project.  The CREWES 
% project may be contacted via email at:  crewesinfo@crewes.org
% 
% The term 'SOFTWARE' refers to the Matlab source code, translations to
% any other computer language, or object code
%
% Terms of use of this SOFTWARE
%
% 1) Use of this SOFTWARE by any for-profit commercial organization is
%    expressly forbidden unless said organization is a CREWES Project
%    Sponsor.
%
% 2) A CREWES Project sponsor may use this SOFTWARE under the terms of the 
%    CREWES Project Sponsorship agreement.
%
% 3) A student or employee of a non-profit educational institution may 
%    use this SOFTWARE subject to the following terms and conditions:
%    - this SOFTWARE is for teaching or research purposes only.
%    - this SOFTWARE may be distributed to other students or researchers 
%      provided that these license terms are included.
%    - reselling the SOFTWARE, or including it or any portion of it, in any
%      software that will be resold is expressly forbidden.
%    - transfering the SOFTWARE in any form to a commercial firm or any 
%      other for-profit organization is expressly forbidden.
%
% END TERMS OF USE LICENSE

if(nargin<4)
	tnot=z(1)/vint(1);
end



if(nargin<3)
	%force column vectors
	vint=vint(:);z=z(:);
	
	% compute a dz vector
	nz=length(z);
	dz=diff(z);

	% integrate
	t1=zeros(size(z));
	t1(2:nz)=cumsum(dz./vint(1:nz-1));

	t1=t1+tnot;
	t2=t1;
else
	%force column vectors
	vint=vint(:);z=z(:);zout=zout(:);
	
	vintout=pcint(z,vint,zout);
	nz=length(z);
	znew=[z(:);zout(:)];
	vnew=[vint(:);vintout(:)];
	[znew,iz]=sort(znew);
	vnew=vnew(iz);

	nz2=length(znew);
	dz=diff(znew);
	tnew=zeros(size(znew));
	tnew(2:nz2)=cumsum(dz./vnew(1:nz2-1));
	tnew=tnew+tnot;

   t=zeros(size(vint));
 	t(iz)=tnew; %unsort
	t1=t(nz+1:length(t));
	t2=t(1:nz);
end