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# RangeVarPlot

class `RangeVarPlot`
  Syntax:

    `RangeVarPlot("rangevar")`

    `RangeVarPlot("expression involving $1")`

  Description:

    Class for making a space plot. eg. voltage as function of path between two points on a cell. For plotting, an object of this type needs to be inserted in a Graph with `g.addobject(rvp)` By default, the location of the path nearest the root is location 0 (the origin) of the space plot.

    If the rangevar does not exist at certain places in the path it is assumed to have a value of 0.

    The first form where rangevar is “v” or “m_hh”, etc. is very efficient since the object can store pointers to the variables for fast plotting.

    The second form is much slower since the expression must be executed by the interpreter for each point along the path for each plot. Execution of the expression is equivalent to `forsec seclist` for (x) f(x) where the expression is the body of f. (Hence the use of $1 to denote the arc length position of the (temporary currently accessed section.)

  See also

  `distance()`

  Example:

    An example is plotting the transfer impedance ratio with

        objectvar imp, rvp, g
        imp = new Impedance()
        rvp = new RangeVarPlot("imp.amp($1)/imp0()")
        rvp... //specify range begin and end
        imp... //specify impedance computation
        g = new Graph()
        g.addobject(*rvp*)

`RangeVarPlot.``begin`()
  Syntax:
    `.begin(x)`
  Description:
    x position of the currently accessed section that starts the path used for the space plot.

`RangeVarPlot.``end`()
  Syntax:
    `.end(x)`
  Description:
    x position of the currently accessed section that ends the path used for the space plot.

`RangeVarPlot.``origin`()
  Syntax:
    `.origin(x)`
  Description:
    x position of the currently accessed section that is treated as the origin (location 0) of the space plot. The default is usually suitable unless you want to have several rangvarplots in one graph in which case this function is used to arrange all the plots relative to each other.

`RangeVarPlot.``left`()
  Syntax:
    `.left()`
  Description:
    returns the coordinate of the beginning of the path.

`RangeVarPlot.``right`()
  Syntax:
    `.right()`
  Description:
    returns the coordinate of the end of the path. The total length of the path is `right() - left()`.

`RangeVarPlot.``list`()
  Syntax:
    `.list(sectionlist)`
  Description:
    append the path of sections to the `SectionList` object argument.

`RangeVarPlot.``color`()
  Syntax:
    `.color(index)`
  Description:
    Change the color property. To see the change on an already plotted RangeVarPlot in a Graph, the Graph should be `flush()`ed.

`RangeVarPlot.``to_vector`()
  Syntax:

    `rvp.to_vector(yvec)`

    `rvp.to_vector(yvec, xvec)`

  Description:
    Copy the range variable values to the `Vector()` yvec. yvec is resized to the number of range points. If the second arg is present then the locations are copied to xvec. A plot of `yvec.line(g, xvec)` would be identical to a plot using `g.addobject(rvp)`.

  See also

  `Graph.addobject()`

`RangeVarPlot.``from_vector`()
  Syntax:
    `rvp.from_vector(yvec)`
  Description:
    Copy the values in yvec to the range variables along the rvp path. The size of the vector must be consistent with rvp.

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