After the FILE keyword, the name of an existing text file containing the data is required. Data are read sequentially from the file regardless of file format: numbers can be in any valid format and be separated by spaces, tabs, or newlines. If the INDEX keyword is specified after the file name, the file is expected to contain multiple columns, and only the one specified by the argument index is read in. A warning is issued if the file does not have the same number of columns throughout. Column indexes start at 0.