Initial price (e.g., 100.0)
Expected return (drift), e.g., 0.05 for 5% annualized
Volatility (e.g., 0.2 for 20%)
Time increment (e.g., 1.0 for daily, or 1/252.0 for trading year)
Number of time steps
double[]: Simulated price series with strictly positive values.
Summary: Generates a time series using Geometric Brownian Motion (GBM), commonly used to model asset prices. Ensures prices are always positive.
Formula: Pt = P[t-1] * exp((mu - 0.5 * sigma^2) * dt + sigma * sqrt(dt) * N(0, 1))