function  d=hypo_forward(m0,xr,v)
% function  hypo_forward
% Input: - Vector m0 with source doordinates and origin time
%        - Matrix xr with dimensions nr x 3, nr is number of receivers
%          times three space coordinates
%        - v velocity 
% Output: Data vector d with nr arrival  times
% 
nr=length(xr(:,1));

for i=1:nr,
    d(i)=m0(4)+ 1./v*sqrt( (xr(i,1)-m0(1))^2 + (xr(i,2)-m0(2))^2 + (xr(i,3)-m0(3))^2);
end

% end