## THERMAL SCIENCE

International Scientific Journal

### Thermal Science - Online First

online first only
### Invariant approaches for the analytic solution of the stochastic Black-Derman toy model

**ABSTRACT**

We work on the analytical solution of the stochastic differential equations (SDEs) via invariant approaches. In particularly, we focus on the stochastic Black-Derman Toy (BDT) interest rate model, among others. After we present corresponding (1+1) parabolic linear partial differential equation (PDE) for BDT-SDE, we use theoretical framework about the invariant approaches for the (1+1) linear PDEs being done in the literature. We show that it is not possible to reduce BDT-PDE into the first and second Lie canonical forms. On the other hand, we success to find transformations for reducing it to the third Lie canonical form. After that, we obtain analytical solution of BDTPDE by using these transformations. Moreover, we conclude that it can be reduced to the fourth Lie canonical form but, to the best of our knowledge, its analytical solution in this form is hard to find yet.

**KEYWORDS**

PAPER SUBMITTED: 2017-11-20

PAPER REVISED: 2017-12-25

PAPER ACCEPTED: 2018-01-10

PUBLISHED ONLINE: 2018-02-18

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