QUADINTERP is the jRidges module of jLab.

 QUADINTERP  Fast quadratic interpolation for arbitrary-sized arrays.
 
    QUADINTERP is a low-level function called by RIDGEINTERP.
 
    XI=QUADINTERP(T1,T2,T3,X1,X2,X3,TI) interpolates a function X
    within an independent variable T using a quadratic algorithm.
 
    The function values X1--X3 may be arrays of any size provided 
    they are all the same size.  The "time" values T1--T3 may be 
    scalars, or arrays of the same size as X1--X3.  
 
    If T1--T3 and X1--X3 are non-scalar arrays, T should either be
    a scalar or an array of the same size as the other arguments.
 
    If T1--T3 and X1--X3 are all scalars, T may be of any size, and
    XI will have the same size as T.
 
    The function values X1--X3 may be real or complex.
 
    QUADINTERP uses the exact algebraic expressions to operate
    looplessly on matrices, thus it is very fast.    
    __________________________________________________________________
 
    Locating maxima or minima
 
    QUADINTERP can also be used to find the extreme value of X(T), 
    that is its maxima or minima.
  
    [XE,TE]=QUADINTERP(T1,T2,T3,X1,X2,X3) with only six input arguments
    solves for TE, the time at which X(T) obtains an extreme value XE.
 
    XE and TE are the same size as the input arrays.
    __________________________________________________________________
 
    Algorithm details
 
    Let X and T be related as
 
               X = A*T.^2 + B*T + C 
 
    The coefficients A, B, and C are uniquely determined by three (T,X)
    pairs.  QUADINTERP solves for these coefficients and uses the 
    result to interpolate X to any other value of T.   
    __________________________________________________________________
 
    See also LININTERP, CUBEINTERP.  
   
    Usage:   x=quadinterp(t1,t2,t3,x1,x2,x3,t);
             [xe,te]=quadinterp(t1,t2,t3,x1,x2,x3);
    __________________________________________________________________
    This is part of JLAB --- type 'help jlab' for more information
    (C) 2006 J.M. Lilly --- type 'help jlab_license' for details

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