4.2.1 Jython Methods
You have seen how to compute wind speed from u and v wind components, using the Formulas facility. IDV formulas are actually code in the Jython language. If your calculations require more than a one-line mathematical expression you can create Jython methods to make calculations then you can call these methods in a formula. Here is an example of computing wind speed with a four-line method.
1. Invoking the Jython Library and Editor
• Click on the main menu item to bring up the `Jython Libraries` Editor

The Jython Library window has two or more panes selected by the tabs at the top. Only the "User's Library" is editable; the others came from the site path and system defaults.

How to Edit in the Jython Library and for more info see How to write a Jython Method and Jython Methods and the IDV

2. Defining your own Jython Method
• In the `Jython libraries` Editor, click on the tab `User's Library`
• Create a new Jython method called windSpeed(u,v). Jython methods have a first line beginning with "def" and ending with the colon ":". The code block composing the method must be indented at least one space. Indentation must be the same for all line in a code block, except continued comment lines which are set off with triple quotes. Your code block will be something like:
```
def  windSpeed(u,v):
"""  compute wind speed from u and v
wind components """
usqd= u*u
vsqd= v*v
ws = sqrt(usqd + vsqd)
return ws
```
• Click on `Save` to check for correct Jython syntax and save the method; you will get an error message if the syntax is not correct. If it is complete, your method is saved.
• Use the menu to exit the editor.
3. Use the Method in a Formula
• Leave up your previous display made with formulas, and the same data source.
• From the main menu, click on . The `Formula Editor` window appears.
• Enter the `Name` `jythonWS`.
• Enter the method for the formula definition in the `Formula` entry field, simply `windSpeed(u,v)`.
• Open the `Advanced` panel by clicking on the down arrow.
• Enter the `Description` "jython wind speed".
• For `Group` select `Workshop` from the drop down list.
• In the `Displays` section, click on `Use selected` and then the `All off` radio button. Then select `Contour Plan View` and `Contour Vertical Cross Section` in the list.
• Click on `Add Formula`.
• An item `jython wind speed` should appear in the `Field Selector` window's `Fields` panel, under the `Workshop` category.
• Use the formula to make a contour display of wind speed using the same u and v wind components from the previous exercise.
• Check to see if the results appear reasonable.