# Re: [idvusers] Pow Command in formula definition

Hi Juan,

Here is what you will need to do:

First define a Jython function (Edit, Formulas, Jython Library, User's
Library).

,----
| def windchill(temp, wspeed):
|     """
|     Windchill formula according to
https://en.wikipedia.org/wiki/Wind_chill
|     """
|     # Must strip off units to make VisAD happy.
|     T = noUnit(temp)
|     WS = noUnit(wspeed)
|     # ** is how you exponentiate, to answer your original question
|     WC = 13.12 + 0.6215 * (T - 273.15) - 11.37 * (WS * 3.6)**0.16 +
0.3965 * (
|         T - 273.15) * (WS * 3.6)**0.16
|     # Reattaching units.
|     return newUnit(WC, "windchill", "celsius")
----

Now go to the Edit, Formulas, Create Formula menu item. The description
and name of the formula are up to you. The formula will be:

,----
| windchill(temperature, windspeed)
----

At this point, load up some data. You will see your new formula in the
IDV Dashboard, Field Selector tab. When you create a display with it,
the IDV will prompt you for the fields you want. Select 3D fields. I
don't think 2D fields will work.

Hope this helps.

Best,

Unidata IDV Support

On Fri, Apr 29, 2016 at 10:08 AM, Juan Figueroa <juanfigueroa@xxxxxxxxxxx>
wrote:

> Hello everyone, I'm trying to calculate the thermal sensation with Siple
> and Passel formula but i dont know how to calculate powers in IDV, the
> equation is:
>
> [image: T_{s}=13,12+0,6215\cdot T-11,37\cdot V^{0,16}+0,3965\cdot T\cdot
> V^{0,16}]
>
> as you can see I need to raise the rate to 0.16 meters per second, can
> someone help?
>
> Thank you.
>
> --
> *- - - - - - - - - - - - - - - - - - - - - - - - - -  - -*
>
> * - - - - - - - - - - - - - - - -  - - - - - - - - - - *
>
> *jn 3:16*
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--
Julien Chastang
Scientific Software Developer
Unidata-UCAR