Leaky Integrate And Fire model with volt units, it is not behaving as it should behave.

LeakyIntegrateAndFire1.py

'''
Created on 2 Nov 2016
@author: io517@york.ac.uk
@link  : http://www.ozturkibrahim.com/
Give a stimulus and see the trajectory of membrane voltage
'''

from brian2 import *
import brian2tools

if __name__ == '__main__':
    OutLyrGroup_NeuronNum     = 1                 # Number of Neurons
    
    ##LIF Neuron dynamics
    lif_taum      =  10 * ms         # membrane time constant (R_m * C_m)
    lif_Vth       = -55 * mV        # threshold potential
    lif_Vresting  = -60 * mV
    lif_Vreset    = -65 * mV         # spike reset, reset potential

    t_simulation  = 200  * ms         #Simulation Time as ms
    t_step        = 0.1               #Time step in simulation  as ms
    t_steps_total = t_simulation / t_step


    #Configuration about the LIF neuron -->
    lif_eqs = '''
        dv/dt      = (v0-v)/taum : volt  (unless refractory)
        v0         = appliedLower + diffIntoLower *int(t > diffTime) : volt 
        appliedLower     : volt
        diffIntoLower    : volt
        diffTime         : second
        taum       : second
    '''
    
    lif_threshold_statement         = 'v > %.2f  * volt' % (lif_Vth)
    lif_reset_statement             = 'v = %.2f  * volt' % (lif_Vreset)
    lif_refractory_time             = 0*ms
    lif_initial_volt_statement      = '%.2f * volt + 0.5 * volt * (%.2f - %.2f)' % (lif_Vreset, lif_Vth, lif_Vreset)
    lif_integ_method                = 'euler'


    OutLyrGroup = NeuronGroup(OutLyrGroup_NeuronNum, lif_eqs,\
                                  threshold  = lif_threshold_statement, \
                                  reset      = lif_reset_statement,     \
                                  refractory = lif_refractory_time,     \
                                  method     = lif_integ_method,        \
                                  #order      = 3,                          \
                                  name       = "OutLyrGroup*")    
        
    OutLyrGroup.v      = 0* volt#lif_initial_volt_statement
    OutLyrGroup.taum   = lif_taum
    
    OutLyrGroup.appliedLower   = lif_Vth - 3*mV
    OutLyrGroup.diffIntoLower  = 6*mV
    OutLyrGroup.diffTime       = 100*ms
    
    SpMon_OutLyrGroup  = SpikeMonitor(OutLyrGroup, name="SpMon_OutLyrGroup*")
    StMon_OutLyrGroup  = StateMonitor(OutLyrGroup, ['v', 'v0'], record=True)
    
    run(t_simulation)
    
    figure(1)
    plot(StMon_OutLyrGroup.t/ms,    StMon_OutLyrGroup.v[0]/mV)
    plot(StMon_OutLyrGroup.t/ms,    StMon_OutLyrGroup.v0[0]/mV)
    xlabel('Time (ms)', fontsize=24)
    
    ylabel('v (mV)',fontsize=24)
    ylim(-70,-50)
    show()
    

LeakyIntegrateAndFire2.py

'''
Created on 2 Nov 2016
@author: io517@york.ac.uk
@link  : http://www.ozturkibrahim.com/
Give a stimulus and see the trajectory of membrane voltage
'''

from brian2 import *
import brian2tools

if __name__ == '__main__':
    OutLyrGroup_NeuronNum     = 1                 # Number of Neurons
    
    ##LIF Neuron dynamics
    lif_taum      =  10 * ms         # membrane time constant (R_m * C_m)
    lif_Vth       = -55              # threshold potential
    lif_Vresting  = -60
    lif_Vreset    = -65         # spike reset, reset potential

    t_simulation  = 200  * ms         #Simulation Time as ms
    t_step        = 0.1               #Time step in simulation  as ms
    t_steps_total = t_simulation / t_step


    #Configuration about the LIF neuron -->
    lif_eqs = '''
        dv/dt      = (v0-v)/taum : 1  (unless refractory)
        v0         = appliedLower + diffIntoLower *int(t > diffTime) : 1 
        appliedLower     : 1
        diffIntoLower    : 1
        diffTime         : second
        taum       : second
    '''
    
    lif_threshold_statement         = 'v > %.2f  ' % (lif_Vth)
    lif_reset_statement             = 'v = %.2f  ' % (lif_Vreset)
    lif_refractory_time             = 0*ms
    lif_initial_volt_statement      = '%.2f  + 0.5  * (%.2f - %.2f)' % (lif_Vreset, lif_Vth, lif_Vreset)
    lif_integ_method                = 'euler'


    OutLyrGroup = NeuronGroup(OutLyrGroup_NeuronNum, lif_eqs,\
                                  threshold  = lif_threshold_statement, \
                                  reset      = lif_reset_statement,     \
                                  refractory = lif_refractory_time,     \
                                  method     = lif_integ_method,        \
                                  #order      = 3,                          \
                                  name       = "OutLyrGroup*")    
        
    OutLyrGroup.v      = 0 #lif_initial_volt_statement
    OutLyrGroup.taum   = lif_taum
    
    OutLyrGroup.appliedLower   = lif_Vth - 3 
    OutLyrGroup.diffIntoLower  = 6 
    OutLyrGroup.diffTime       = 100*ms
    
    SpMon_OutLyrGroup  = SpikeMonitor(OutLyrGroup, name="SpMon_OutLyrGroup*")
    StMon_OutLyrGroup  = StateMonitor(OutLyrGroup, ['v', 'v0'], record=True)
    
    run(t_simulation)
    
    figure(1)
    plot(StMon_OutLyrGroup.t/ms,    StMon_OutLyrGroup.v[0])
    plot(StMon_OutLyrGroup.t/ms,    StMon_OutLyrGroup.v0[0])
    xlabel('Time (ms)', fontsize=24)
    
    ylabel('v (mV)',fontsize=24)
    ylim(-70,-50)
    show()
    

Both codes are exactly the same except units. Second code is working as it should. However, the first one with units (mV - volt) should also work but it is behaving strangely. Dont understand what is the problem in the first file.

Solution is suggested by Dan Goodman >>
The problem is '%.2f * volt' % V_th gives result '0.06 * volt' as the output because 55 mV in volts is 0.055 and you only give 2 decimal places so it gets rounded to 0.06.