def fold_change(c, RK, KdA=0.017, KdI=0.002, Kswitch=5.8):
    """ Function computes the theoretical fold change in repression."""
    # Compute fold change
    fold_change = (1 + RK*((1+c/KdA))**2/((1+c/KdA)**2 + Kswitch*(1+c/KdI)**2))**(-1)
    # Return concentration array and fold change array
    return fold_change