gd geta the data from a file. Data should be in an ascii file with between two and 20 columns. Actually, you can have as many columns as you want in the file, but the program will only read up to 20. For fitting functions of more than one independent variable, select a function with the number of independent variables that you want to fit to before reading in data. This will allow the program to default to interpreting columns 1 through n (where n is the number of independent variables of the current function) as representing the independent variables in order. By default, the (n+1)th column is interpreted to be y(x0 ... xn) and the (n+2)th column is interpreted as the experimental error in the measured y. If you wish to assign the columns in your data file differently, or if you read in the data before choosing a function (for more than 1 independent variable), you will have to use the order command.
By default, if no function has been selected, or if a function of one independent variable has been selected, the first column is x, the second is y, and if there is a third, it is assumed to be the error in y. If you wish to assign different columns to be x, y, and δy, use the order command. By default, the program can handle a file with five columns and 1024 rows. The ad command can be used to allocate the data array differently and handle up to 23 columns and as many rows as memory allows.
Lines in a data file beginning with the # character are taken
to be comments.