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Hi all,

I have a very basic question of how to change 'dt' in 'RunControl' panel of NEURON GUIs. Currently I am using either Implicit Fixed Step or C-N Fixed Step mode for my simulation and trying to manually change the value of 'dt' to see the effects of varying ‘dt’. I could not change even the default value (i.e. 0.025) of 'dt' in either modes. I might miss something here, but I could not find the way of changing the value of 'dt' anywhere in NEURON website. Is there anybody who can help me? Thanks.

Good question.

dt specifies the integration step size. NEURON's standard run system also has a parameter called steps_per_ms that controls the intervals at which points are plotted to graphs; its numerical value is shown in the field next to the "Points plotted/ms" button. Clearly these two parameters must be compatible, i.e. the interval between two points on a graph must contain a whole number of time steps. The design decision was that steps_per_ms would govern dt. It does this by means of a standard run system procedure called setdt() that adjusts dt as necessary whenever any of the following happens:
--changing the contents of the numerical field next to the "dt" or "Points plotted/ms" button
--calling stdinit()
--calling run()

Thank you so much Ted. Your explanation was very helpful to me.

And helpful to others, now that the question & answer are visible to all.