What is the matrix.txt file on my SD card? Is it safe to delete? I have a file called matrix.txt at the root of my SD card.

It is a text file that contains the serialization of a matrix of floats.

What is this file? Can I delete it?
The Android OS itself is not dependant on any files on the removable SD card. If you have no apps that use this file, you can safely delete the file, or even format the SD card if you want.