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Advanced Proof

The Cox-Ingersoll-Ross (CIR) Model: Ensuring Positivity and Bond Valuation

Students often confuse CIR volatility with the Vasicek model. In Vasicek, volatility is constant, allowing rates to become negative. In CIR, the rt \sqrt{r_t} term ensures volatility vanishes at the origin. Another pitfall is neglecting the Feller condition, which is strictly required to prevent the process from reaching zero.
Institutional Reference: Advanced Stochastic Processes
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