NMODL “pointers”

Mechanisms can refer to values in other mechanisms, e.g. the sodium current ina. Therefore, it supports a notion of “pointer”, called Datum. A datum can store a pointer to a double, a stable pointer to a double, integers, or pointers to anything else.

Integer Variables

One important subset of Datum are pointers to RANGE variables. Meaning they are pointers to parameters in other mechanisms or pointers to the parameters associated with each node, e.g. the voltage. Since the storage of RANGE variable is controlled by NEURON/CoreNEURON, these pointers have stronger semantics than a double*.

These make up the majority of usecases for Datum; and are considered the well-mannered subset.

In CoreNEURON this subset of Datums are treated differently for other Datums. Because CoreNEURON stores the values these Datums can point to in a single contiguous array of doubles, the “pointers” can be expressed as indices into this array.

Therefore, this subset of Datums is referred to as “integer variables”.

In NEURON these pointers are a data_handle to the value they point to. Before the simulation phase they are “resolved” and a cache stores a list of double* to the appropriate values.