# Grapher¶

A tool for graphing any set of expressions as a function of an independent variable.

The Grapher is similar to a “for” statement. It iterates the independent variable over the range specified by the “Indep Begin” and “Indep End” field editors using “Steps” steps. At each step, it executes the statements specified in the Generator field (if any), and plots the values that are specified in the Graph scene from the PlotWhat menu item at the x-axis location specified by the value of the “X-expr” (normally the same as the independent variable).

These y values and X-expr can be variable names or function names.

To pop up the widget say:

```
h.load_file("grapher.hoc") # reads this file
h.makegrapher(1) # pop up a new grapher
```

Creating a grapher using

```
h.makegrapher()
```

pops up a short form of the Grapher without “Indep Begin”, “Indep End”, or “X-expr” buttons. The limits are defined by the x-axis length of the current view.

Graphers may be saved in a .ses file.

To use the grapher widget:

- enter the independent variable name (press the button) eg. x
- enter the begin, end, and steps values.
- specify the y variables: in the graph panel press the left button and select “Plot What?” and enter a HOC expression or variable to plot. eg. sin(x) You can do this several times to plot several expressions.
- If the y variables are actual functions of the independent variable press the Plot button to see the plot. If the y variables are in fact just variables then you will need a generator statement that tells how to compute the y variables given a value of the independent variable. eg. Just for fun you can try entering the generator statement:
`print x, sin(x)`

Example:

```
Example 1: plot sin(t)
1) PlotWhat: sin(t)
2) Plot
Example 2: plot of steady state m process in nrniv
1) Independent Var: x
2) Generator: rates_hh(x)
3) IndepBegin -100, Indep End 50
4) Set View: x: -100 50 y: 0 1
5) PlotWhat: minf_hh
6) Plot
Example 3: In context of Neuron Main Menu simulation
0) pop up grapher by selecting appropriate "New Graph" submenu item.
1) Independent Var: v_init
2) Generator: init()
3) IndepBegin -100, Indep End 50
4) SetView: x: -100 50 y:cancel
5) PlotWhat: <any set of variables in any section>
6) Plot
Example 4: peak inward current during voltage clamp
Replace the standard: proc advance() {fadvance()} with a procedure
that stores the peak inward current (and possibly sets stoprun=1
when you are past the peak). Then in the Grapher set Steps to 20
the independent variable to the voltage clamp amplitude and the
generator to run().
```

## Plot¶

For each value of the independent variable the generator statement is executed (if it exists) and the PlotWhat expressions are plotted.

## EraseAll¶

Removes all expressions from the graph.

## Steps¶

Number of independent variable values used to make the graph. For the small grapher, the range of the independent variable is the length of the x-axis.

## IndependentVar¶

Dialog appears requesting the variable to be used as the independent variable (default t). If the variable is undefined it will be created.

## Generator¶

A statement to be executed after setting a value of the independent variable but before plotting the expressions. This allows plotting of variables that depend implicitly on the independent variable.

## IndepBegin¶

For a grapher made with `h.makegrapher(1)`

, specifies initial value
of the independent variable.

## IndepEnd¶

Specifies final value of independent variable.

## Xexpr¶

A grapher made with `h.makegrapher(1)`

allows separate specification of
independent variable and the x axis plot functions. This allows
phase plane plots. The Xexpr may be any function of the independent
variable or an implicit function if a generator statement exists.