function vint=vrms2vint(vrms,t,flag)
% VRMS2VINT: convert rms to interval velocity
%
% vint=vrms2vint(vrms,t,flag)
% vint=vrms2vint(vrms,t)
%
% flag=0 ... return nonphysical interval velocities as NaN
%     =1 ... interpolate interval velocities from neighbors to
%            replace non-physical results
%  ******* default = 0 **********
%
% 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,
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% Terms of use of this SOFTWARE
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if(nargin<3)
	flag=0;
end

%force column vectors
vrms=vrms(:);
t=t(:);

%compute interval velocity squared
vint=zeros(size(vrms));
nt=length(t);
i1=1:nt-1;i2=2:nt;
vrms2=vrms.^2;
vint(i1)= (vrms2(i2).*(t(i2)-t(1))-vrms2(i1).*(t(i1)-t(1)))./(t(i2)-t(i1));
%find and process non-physical ones
ind=find(vint<0);
if(~isempty(ind))
	if(flag)
		ilive=find(vint>0);
		vint(ind)=interpextrap(t(ilive),vint(ilive),t(ind));
	else
		vint(ind)=nan*ones(size(ind));
	end
end
%compute interval velocity
vint=sqrt(vint);
vint(nt)=vint(nt-1);