# The Hodgkin-Huxley model of a space-clamped axon.  This is the classic model of an excitable membrane and
# shows the standard action potential for proper parameters.  This particular form is from Keener and Sneyd (1998).
#
#  Variables:
#     v : Voltage difference across the membrane.
#     m : Na activation variable.  Basically describes the activity of voltage-gated Na channels.
#     n : K activation variable.
#     h : Na inactivation variable.
#
#  Parameters:
#     Cm  : Membrane capacitance
#     gK  : K conductance constant
#     gNa : Na conductance constant
#     gL  : Leakage conductance constant
#     vK  : Equilibrium K potential
#     vNa : Equilibrium Na potential
#     vL  : Equilibrium leakage potential
#     Ia  : Applied current
#------------------------------------------------------------------------------------------------------------
# Set-up equations:
alm = 0.1*(25-v)/(exp((25-v)/10)-1)
bem = 4*exp(-v/18)
alh = 0.07*exp(-v/20)
beh = 1/(exp((30-v)/10)+1)
aln = 0.01*(10-v)/(exp((10-v)/10)-1)
ben = 0.125*exp(-v/80)
#------------------------------------------------------------------------------------------------------------
# Vector field:
v' = (-gK*(n^4)*(v-vK)-gNa*(m^3)*h*(v-vNa)-gL*(v-vL)+Ia)/Cm
m' = alm*(1-m)-bem*m
n' = aln*(1-n)-ben*n
h' = alh*(1-h)-beh*h
#-------------------------------------------------------------------------------------------------------------
# Parameters:
p Cm=1, gK=36, gNa=120, gL=0.3, vK=-12, vNa=115, vL=10.6, Ia=10
#-------------------------------------------------------------------------------------------------------------
# Initial conditions: 
I v=-20, m=0.05, n=0.6, h=0.6
#-------------------------------------------------------------------------------------------------------------
# Control stuff
@ bounds=100000, total=20, delay=10, Xlo=0, Xhi=20, Ylo=-30, Yhi=120, MaxStore=1000000
d