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# Ions

`ion_style`()
  Syntax:

    `oldstyle = ion_style("name_ion", c_style, e_style, einit, eadvance, cinit)`

    `oldstyle = ion_style("name_ion")`

  Description:

    In the currently accessed section, force the named ion (eg. na_ion, k_ion, ca_ion, etc) to handle reversal potential and concentrations according to the indicated styles. You will not often need this function since the style chosen automatically on a per section basis should be appropriate to the set of mechanisms inserted in each section.

    Warning: if other mechanisms are inserted subsequent to a call of this function, the style will be "promoted" according to the rules associated with adding the used ions to the style previously in effect.

    The oldstyle value is previous internal setting of c_style + 4*cinit + 8*e_style + 32*einit + 64*eadvance.

    c_style: 0, 1, 2, 3.
      Concentrations respectively treated as UNUSED, PARAMETER, ASSIGNED, or STATE variables. Determines which panel (if any) will show the concentrations.
    e_style: 0, 1, 2, 3.
      Reversal potential respectively treated as UNUSED, PARAMETER, ASSIGNED, or STATE variable.
    einit: 0 or 1.
      If 1 then reversal potential computed by Nernst equation on call to `finitialize()` using values of concentrations.
    eadvance: 0 or 1.
      If 1 then reversal potential computed every call to `fadvance()` using the values of the concentrations.
    cinit: 0 or 1.
      If 1 then a call to finitialize() sets the concentrations to the values of the global initial concentrations. eg. `nai` set to `nai0_na_ion` and `nao` set to `nao0_na_ion`.

    The automatic style is chosen based on how the set of mechanisms that have been inserted in a section use the ion. Note that the precedence is WRITE > READ > unused in the USEION statement; so if one mechanism READ's cai/cao and another mechanism WRITE's them then WRITE takes precedence in the following table. For compactness, the table assumes the ca ion. Each table entry identifies the equivalent parameters to the ion_style function.

    > cai/cao -> | unused | read | write
    > --- | --- | --- | ---
    > eca unused | 0,0,0,0,0 | 1,0,0,0,0 | 3,0,0,0,1
    > eca read | 0,1,0,0,0 | 1,2,1,0,0 | 3,2,1,1,1
    > eca write | 0,2,0,0,0 | 1,2,0,0,0 | 3,2,0,0,1

    For example suppose one has inserted a mechanism that READ's eca, a mechanism that READ's cai, cao and a mechanism that WRITE's cai, cao Then, since WRITE takes precedence over READ in the above table, `cai/cao` would appear in the STATE variable panel (first arg is 3), `eca` would appear in the ASSIGNED variable panel (second arg is 2), `eca` would be calculated on a call to finitialize (third arg is 1), `eca` would be calculated on every call to fadvance (fourth arg is 1), `cai/cao` would be initialized (on finitialize) to the global variables `cai0_ca_ion` and `cao0_ca_ion` respectively. (note that this takes place just before the calculation of `eca`).

`ion_register`()
  Syntax:
    `type = ion_register("name", charge)`
  Description:
    Create a new ion type with mechanism name, "name_ion", and associated variables: iname, nameo, namei, ename, diname_dv. If any of these names already exists and name_ion is not already an ion, the function returns -1, otherwise it returns the mechanism type index. If name_ion is already an ion the charge is ignored but the type index is returned.

`ion_charge`()
  Syntax:
    `charge = ion_charge("name_ion")`
  Description:
    Return the charge for the indicated ion mechanism. An error message is printed if name_ion is not an ion mechanism.

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