It is commonly necessary to do operations on some or all of the elements of a dataset independently (pixels in an image). For example, in the reduction of raw data it is necessary to subtract the Sky value (Sky value) from each image image. Later (once the images as warped into a single grid using Warp for example, see Warp), the images are co-added (the output pixel grid is the average of the pixels of the individual input images). Arithmetic is Gnuastro’s program for such operations on your datasets directly from the command-line. It currently uses the reverse polish or post-fix notation, see Reverse polish notation and will work on the native data types of the input images/data to reduce CPU and RAM resources, see Numeric data types. For more information on how to run Arithmetic, please see Invoking Arithmetic.