multiplication or squaring of variables

[Emilio Mayorga]

I want to create a new variable, wind speed, from the u and v components: speed = (u^2 + v^2)^0.5. Can NCO do this? I've looked through the Manual and can't find anything relevant; ncflint doesn't multiply two variables. I also looked through the examples in the test battery file, but found nothing.

Can NCO do it?

Thanks.

Emilio Mayorga

[Nobody/Anonymous]

I believe NCO can do this in 5--10 commands.
Use ncwa -v u -w u and turn off normalization.
That should get you u^2. Do the same for v^2.
Add the two using ncdiff and subtracting -v^2.
How do you get -v^2? subtract v^2 from itself
twice. you'll need to use ncrename in order
to get u^2 + v^2. Then just use ncwa -y sqrt.
Disclaimer: this may work better in my head
than it does in practice. Good luck.

[Emilio Mayorga]

Thanks for the tip (Charlie? I don't know who wrote that reply). I can see where it's going. I tested ncwa -N -v u -w u, but got Segmentation Fault every time (I tried changing the averaging dimensions specified with -a). The variable is short int-type, and has a scale_factor and add_offset. Looking at the data-type conversion section in the Manual, it seems possible that trying to square a short int while saving the result as the same data type may create an out-of-bounds problem.

I'd be interested in hearing your opinion on this, but I've found a way of accomplishing my task using Ferret instead of NCO. Thanks. -Emilio

[Charlie Zender]

It is dying because NCO does not handle packed data.

Charlie

[Emilio Mayorga]

Thanks, Charlie. I thought the packing attributes would just be ignored. -Emilio