I have an array of data which shows a map of Sweden (the sea is masked out so all the values over the sea are set to 0). I need to calculate the root mean square of only the values not equal to 0 in my array, but I have no idea how to do this in Matlab. I can calculate the RMS of the whole array, but it comes out far too good (due to all the zeros over the sea!).

So if I have a 70x40 array how do I only pick out the values not equal to zero and take the RMS of them?

Help would be much appreciated.

A