There are N particles that can move in one dimension. During one time step a particle can move one particle width to the left with probability pLeft, or to the right with probability pRight.

• The probabilities sum to 1 and the difference between pRight and pLeft is referred to as the drift velocity.
• Particles move in discrete units of distance equal to one particle width.
• Particles may not occupy the same position at the same time.
• Particles are initialized one particle-width apart from one another.

The simulation tracks the center of mass (COM) of the N particles and records the time where the COM has traveled a threshold distance L.

There are two implementations, one in fortran and the other in python. Both seem to produce similar results.