# Having problem on set external current input

**URL:** <https://brian.discourse.group/t/having-problem-on-set-external-current-input/1364>\
**Category:** Support\
**Created:** [3 January 2025 08:52 UTC](https://brian.discourse.group/t/having-problem-on-set-external-current-input/1364 "2025-01-03T08:52:02Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Bolloknoon](https://yyz2.discourse-cdn.com/free1/user_avatar/brian.discourse.group/bolloknoon/32/388_2.png) [@Bolloknoon](https://brian.discourse.group/u/Bolloknoon)\
**Post date:** [3 January 2025 08:52 UTC](https://brian.discourse.group/t/having-problem-on-set-external-current-input/1364/1 "2025-01-03T08:52:02Z")

</div>

I wanna make simulation about external hyperpolarization current.

Main intention for this code is making hyperpolarization current on subpopulation of inhibitory neurons.

**Minimal code to reproduce problem**

```auto
from brian2 import *
import numpy as np
import random
import math
import multiprocessing
import time

'''inhibitory neuron'''

Cm = 1 * uF # /cm**2

EL = -65 * mV
ENa = 55 * mV
EK = -90 * mV
gNa = 100 * msiemens
gK = 40 * msiemens

'''synapse decay time constant'''

t_ampa = 2 * ms
t_gaba = 4 * ms
t_gaba_sst = 12 * ms
t_gaba_ngfc = 20 * ms

eqs = '''
            dv/dt = (-gNa*m**3*h*(v-ENa) -gK*n**4*(v-EK) -gL*(v-EL) - gKZ*z*(v-EK)- I_ext) / Cm : volt 

            I_ext = g_ampa*(v-V_AMPA) + g_gaba*(v-V_GABA) + g_gaba_sst*(v-V_GABA) + I_photo: amp
            I_photo:amp
            dg_ampa/dt = -g_ampa/ t_ampa : siemens
            dg_gaba/dt = -g_gaba/ t_gaba : siemens
            dg_gaba_sst/dt = -g_gaba_sst/ t_gaba_sst : siemens
            dg_gaba_ngfc/dt = -g_gaba_ngfc/ t_gaba_ngfc : siemens
            m = alpham/(alpham+betam) : 1
            alpham = -0.1/mV*(v+30*mV)/(exp(-0.1/mV*(v+30*mV))-1)/ms : Hz
            betam = 4*exp(-(v+55*mV)/(18*mV))/ms : Hz
            dh/dt = 0.2*(alphah*(1-h)-betah*h) : 1
            alphah = 0.7*exp(-(v+44*mV)/(20*mV))/ms : Hz
            betah = 10/(exp(-0.1/mV*(v+28*mV))+1)/ms : Hz
            dn/dt = 0.2*(alphan*(1-n)-betan*n) : 1
            alphan = -0.1/mV*(v+34*mV)/(exp(-0.1/mV*(v+34*mV))-1)/ms : Hz
            betan = 1.25*exp(-(v+44*mV)/(80*mV))/ms : Hz
            dz/dt = (z_inf - z)/(60*ms) : 1
            z_inf = 1/(1+exp(-0.7*((v/(1 * mV) + 30)))) : 1
    '''

L_4_i = NeuronGroup(150, eqs, threshold='v>-48.8*mV', refractory='v>-48.8*mV', method='rk4')

L_4_i.namespace['gL'] = 0.1 * msiemens
L_4_i.namespace['gKZ'] = 0 * msiemens

for i in range(150):
    trans_ratio=0.5
    if(i < 150 * trans_ratio):
        L_4_i.namespace['I_photo'][i]= (-3.0 + 2.0 * random.random()) * 10**(-3) * mA
    else:
        L_4_i.namespace['I_photo'][i]= 0 *10**(-3) * mA

L_4_i.v = EL
L_4_i.h = 1

''' excitatory neuron '''

L_4_e = NeuronGroup(1600, eqs, threshold='v>-39.7*mV', refractory='v>-39.7*mV', method='rk4')

L_4_e.namespace['gL'] = 0.1 * msiemens
L_4_e.namespace['gKZ'] = 0.5 * msiemens

L_4_e.v = EL
L_4_e.h = 1

```

**The error occurs** :

```auto
ERROR Brian 2 encountered an unexpected error. If you think this is a bug in Brian 2, please report this issue either to the discourse forum at <http://brian.discourse.group/>, or to the issue tracker at <https://github.com/brian-team/brian2/issues>. Please include this file with debug information in your report: C:\Users\omokn\AppData\Local\Temp\brian_debug_98mx2ghb.log Additionally, you can also include a copy of the script that was run, available at: C:\Users\omokn\AppData\Local\Temp\brian_script_kkqmaob1.py Thanks! [brian2]
Traceback (most recent call last):
  File "C:\Users\omokn\OneDrive\바탕 화면\project\exp_trash.py", line 57, in <module>
    L_4_i.namespace['I_photo'][i]= (-3.0 + 2.0 * random.random()) * 10**(-3) * mA
    ~~~~~~~~~~~~~~~ ^^^^^^^^^^^
KeyError: 'I_photo'

```

I think I make several mistakes on handling namespace of neuron population. How can I fix these problem?

---

<div class="post-metadata">

**Author:** ![mstimberg](https://yyz2.discourse-cdn.com/free1/user_avatar/brian.discourse.group/mstimberg/32/11_2.png) [@mstimberg](https://brian.discourse.group/u/mstimberg)\
**Post date:** [3 January 2025 16:42 UTC](https://brian.discourse.group/t/having-problem-on-set-external-current-input/1364/2 "2025-01-03T16:42:06Z")

</div>

Hi @Bolloknoon. This use of the `namespace` is indeed not quite correct. You can use the `namespace` to set external scalar constants – you’d typically specify this as the `namespace` argument to `NeuronGroup`, but your approach should work as well. Note that you can also replace values directly in the equations (basically doing string replacement for you), e.g. with `... NeuronGroup(150, Equations(eqs, gL=0.1*mS, gKZ=0*mS), ...)`.

The situation for `I_photo` is different, because it is not a scalar constant, but a vector. Since you have – correctly – added `I_photo` to your equations, you should assign to it with `L_4_i.I_photo = …` directly, instead of using the `namespace`.  
Note that in general it is more efficient to not use a loop but instead assign a single array. In your case, you could either use numpy’s array operations, or Brian’s builtin language – both should give the same result here:

```python
# Using a numpy array
L_4_i.I_photo[:int(150*trans_ratio)] = (-3.0 + 2.0 * np.random.rand(int(150*trans_ratio))) * uA

```

A bit more compact using Brian’s own language:

```python
L_4_i.I_photo['i<150*trans_ratio'] = '(-3.0 + 2.0 * rand()) * uA'

```

---

<div class="post-metadata">

**Author:** ![Bolloknoon](https://yyz2.discourse-cdn.com/free1/user_avatar/brian.discourse.group/bolloknoon/32/388_2.png) [@Bolloknoon](https://brian.discourse.group/u/Bolloknoon)\
**Post date:** [3 January 2025 16:47 UTC](https://brian.discourse.group/t/having-problem-on-set-external-current-input/1364/3 "2025-01-03T16:47:10Z")

</div>

I recognized right a minute before answer but I don’t exactly know why. Thanks for detailed explanation!

I self-solved this problem as:

```auto
    for i in range(150):
        if i < (150*trans_ratio):
            L_4_i.I_photo[i] = (-3.0 + 2.0 * random.random()) * 10**(-3) * mA
        else:
            L_4_i.I_photo[i] = 0 * mA

```

But your code make this more compact than I thought.