Impedance

classes
   compute        input_phase    ratio          transfer_phase  
   input          loc            transfer       
For calculating input and transfer impedances at an instant of time Usage involves first defining a location either for the current stimulus or else the voltage measuring electrode, then computing the global transfer and input impedance function at a particular frequency, then retrieving values of the complex transfer and input impedance.


loc

Impedance

SYNTAX

.loc(x)

DESCRIPTION

A fixed current stimulus or voltage electrode location at position 0<=x<=1 of the currently accessed section. This is needed for the transfer impedance calculation. Note that transfer impedances obey the relation v(x)/i(loc) == v(loc)/i(x) where loc is the fixed location and x ranges over every position of every section.


compute

Impedance

SYNTAX

.compute(freq)

DESCRIPTION

Transfer impedance between location specified above and any other location is computed. Also the input impedance at all locations is computed -- v(x)/i(x) Frequency specified in Hz. All membrane conductances are computed and used in the calculation as if fcurrent() was called. The compute call is expensive but as a rule of thumb is not as expensive as fadvance().


transfer

Impedance

SYNTAX

.transfer(x)

DESCRIPTION

absolute amplitude of the transfer impedance between the position specified in the loc(x) call above and 0<=x<=1 of currently accessed section at the freq specified by a previous compute(freq). The value returned can be thought of as either |v(loc)/i(x)| or |v(x)/i(loc)| Probably the more useful way of thinking about it is to assume a current stimulus of 1nA injected at x and the voltage in mV recorded at loc.

Return value has the units of Megohms and can be thought of as the amplitude of the voltage (mV) at one location that would result from the injection of 1nA at the other.


input

Impedance

SYNTAX

.input(x)

DESCRIPTION

absolute amplitude of v(x)/i(x) of the currently accessed section


ratio

Impedance

SYNTAX

.ratio(x)

DESCRIPTION

|v(loc)/v(x)| Think of it as voltage clamping to 1mV at x at some frequency and recording the voltage at loc.


transfer_phase

Impedance

SYNTAX

.transfer_phase(x)

DESCRIPTION

phase of transfer impedance. The phase is modulo 2Pi in the range -Pi to +Pi so as one moves away from the loc remember that the actual phase can become less than -Pi. If the amplitude is very small the phase may be inaccurate and cannot be computed at all if the amplitude is 0.


input_phase

Impedance

SYNTAX

.input_phase(x)

DESCRIPTION

phase of input impedance.

Note: Impedance makes heavy use of memory since four complex vectors are allocated with size equal to the total number of segments. After compute is called two of these vectors holds the input and transfer impedance for a given loc, freq, and neuron state. Because of the way results of calculations are stored it is very efficient to access amp and phase; reasonably efficient to change freq or loc, and inefficient to vary neuron state, eg, diameters. The last case implies at least the overhead of a call like fcurrent().(actually the present implementation calls fcurrent() on every compute() call but that could be fixed if increased performance was needed).


neuron/neuron/classes/impedanc.hel : Dec 19 1996