to find the x-intercept value of X(T).
  
    TO=<a href="lininterp.html">LININTERP</a>(T1,T2,X1,X2) with only four input arguments returns TO,
    the time at which X(T) vanishes.
 
    TO is the same size as the input arrays.
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    Algorithm details
 
    Let X and T be related as
 
               X = A*T + B 
 
    The coefficients A and B are uniquely determined by two (T,X) pairs.  
    <a href="lininterp.html">LININTERP</a> solves 