We study the microbunching instability in a bunch compressor by a parallel code with some improved numerical algorithms. The two-dimensional charge/current distribution is represented by a Fourier series. with coefficients determined through Monte Carlo sampling over an ensemble of tracked points. This gives a globally smooth distribution with low noise. https://www.alarecre.com/Looney-Tunes-Marvin-the-Martian-Big-Head-Galaxy-S23-Waterproof-Case-p116784/