: $Id: izap.mod,v 1.4 2015/05/28 02:42:00 ted Exp ted $
COMMENT
izap.mod
Delivers an oscillating current that starts at t = del >= 0.
The frequency of the oscillation increases linearly with time
from f0 at t == del to f1 at t == del + dur,
where both del and dur are > 0.
Uses event delivery system to ensure compatibility with adaptive integration.
Original implementation 12/4/2008 NTC
ENDCOMMENT
NEURON {
POINT_PROCESS Izap
RANGE del, dur, f0, f1, amp, f, i
ELECTRODE_CURRENT i
}
UNITS {
(nA) = (nanoamp)
PI = (pi) (1)
}
PARAMETER {
del (ms)
dur (ms)
f0 (1/s) : frequency is in Hz
f1 (1/s)
amp (nA)
}
ASSIGNED {
f (1/s)
i (nA)
on (1)
}
INITIAL {
f = 0
i = 0
on = 0
if (del<0) { del=0 }
if (dur<0) { dur=0 }
if (f0<=0) { f0=0 (1/s) }
if (f1<=0) { f1=0 (1/s) }
: do nothing if dur == 0
if (dur>0) {
net_send(del, 1) : to turn it on and start frequency ramp
}
}
COMMENT
The angular velocity in radians/sec is w = 2*PI*f,
where f is the instantaneous frequency in Hz.
Assume for the moment that the frequency ramp starts at t = 0.
f = f0 + (f1  f0)*t/dur
Then the angular displacement is
theta = 2*PI * ( f0*t + (f1  f0)*(t^2)/(2*dur) )
= 2*PI * t * (f0 + (f1  f0)*t/(2*dur))
But the ramp starts at t = del, so just substitute tdel for every occurrence of t
in the formula for theta.
ENDCOMMENT
BREAKPOINT {
if (on==0) {
f = 0
i = 0
} else {
f = f0 + (f1  f0)*(tdel)/dur
i = amp * sin( 2*PI * (tdel) * (f0 + (f1  f0)*(tdel)/(2*dur)) * (0.001) )
}
}
NET_RECEIVE (w) {
: respond only to selfevents with flag > 0
if (flag == 1) {
if (on==0) {
on = 1 : turn it on
net_send(dur, 1) : to stop frequency ramp, freezing frequency at f1
} else {
on = 0 : turn it off
}
}
}
