Trinomial Tree
Also called: trinomial lattice, three-branch tree
A trinomial tree lets each node move up, down or sideways, giving an extra degree of freedom over a binomial tree. That freedom is what allows mean reversion and time-dependent parameters to be built in cleanly, which is why interest-rate models like Hull-White are usually implemented this way. Convergence is faster and smoother than binomial for the same number of steps, at modest extra cost.
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