SigmaPointsChol:

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   UKF sigma points using chol.

   See UKFWeight for definitions of alpha and kappa

   Since version 11.
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   Form:
   d = SigmaPointsChol( d, p )
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   ------
   Inputs
   ------
   d             (1,1)   Data structure
                         .cSqrt	(1,1) sqrt(alpha^2*(length(x) + kappa))

   p             (n,n)  Covariance matrix

   -------
   Outputs
   -------
   d             (1,1)   Data structure
                         .xA       (:,:) Sigma points

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   Reference: Simo Sarkka, "Bayesian Estimation of Time-Varying Systems:
              Discrete-Time Systems, Version 1.3 (March 2, 2012).
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