www.neuron.yale.edu

Hi.
I tried running my first NEURON program copied from “A NEURON Programming Tutorial - Part Aâ€

One possibility is that the model has no default section.
NEURON Main Menu / Greph / Voltage axis
creates a graph whose plot list contains the variable v(.5). If there is no
default section, NEURON will not know which section v belongs to. Assuming
that the model has a "top level" section called soma (in practical terms,
this means that "soma" is not part of an object, i.e. was not created by a
create statement inside a template), the fix is to execute the statement
access soma
before you create any voltage axis graph. A good place for the access
statement is immediately after the "create" statement that creates the
soma section.

If the soma is _not_ top level but is a public member of a class--in which
case the cell was created by creating a new instance of the class, as in
this example
objref cell
cell = new Pyr()
--the fix is to execute the statement
access cell.soma
before you create any voltage axis graph.

To avoid confusion, it is best to use only one access statement in a
program. If it is necessary to plot v in more than one section, it is
necessary to use the full name of the variable, e.g.
soma.v(0.5)
dend[21].v(0.1)
for single cell models, and
pyr[4].axon[3].v(0.1)
etc.
for models with more than one cell.

thank you so much for your kind help. I have plotted the results successfully.