function z=linterp(k,z0,z)
% linterp - linear interpolation between values
%
% linterp :: 
%    [Size] ~'fraction of distance to travel from from initial to final point',
%    [Size] ~'initial point',
%    [Size] ~'final point'
% -> [Size] ~'interpolated point'.

z = z0+k.*(z-z0);
