new_contents: import numpy as np
  import matplotlib.pyplot as plt
  import rsf
  
  model = rsf.ExternalSystem()
  
  # Set model initial conditions
  model.mu0 = 0.6 # Friction initial (at the reference velocity)
  model.a = 0.005 # Empirical coefficient for the direct effect
  model.k = 1e-3 # Normalized System stiffness (friction/micron)
  model.v = 1. # Initial slider velocity, generally is vlp(t=0)
  model.vref = 1. # Reference velocity, generally vlp(t=0)
  
  state1 = rsf.DieterichState(model)
  state1.b = 0.01  # Empirical coefficient for the evolution effect
  state1.Dc = 10.  # Critical slip distance
  
  state2 = rsf.DieterichState(model)
  state2.b = 0.001  # Empirical coefficient for the evolution effect
  state2.Dc = 5.  # Critical slip distance
  
  model.state_relations = [state1,state2] # Which state relation we want to use
  
  # We want to solve for 40 seconds at 100Hz
  model.model_time = np.arange(0,40.01,0.01)
  
  # We want to slide at 1 um/s for 10 s, then at 10 um/s for 31
  lp_velocity = np.ones_like(model.model_time)
  lp_velocity[10*100:] = 10. # Velocity after 10 seconds is 10 um/s
  
  # Set the model load point velocity, must be same shape as model.model_time
  model.loadpoint_velocity = lp_velocity
  
  # Run the model!
  solver = rsf.RateState()
  solver.solve(model)
  
  # Make the phase plot
  solver.phasePlot(model)
  
  # Make a plot in displacement
  solver.dispPlot(model)
  
  # Make a plot in time
  solver.timePlot(model)
  
subject: Add two state variable example