order assigns significance to the columns in the internal data matrix. When a data file is read with the gd command, the first column in the file is stored in the data[0]. (The 0th column of an 2-D array). The second column is stored in data[1], etc. By default, these columns are interpteted in a certain way (See the gd command). The order command is used to change the default behavior.
Errors in the independent variables can be used in the fit by using techniques of error propagation to calclate a corresponding error in y. That is:
Examples for one independent variable:
order 2 1 0 x0 is the third column in the file, y is the second column, σy is the first column.
order 1 4 x0 is the second column, y is the fifth column, σy is not specified.
order 0 1 2 3 x0 is the first column in the file, y is the second column, σy is the third column, σx0 is the fourth column and is used in the fit.
order 0 1 2 -1 x0 is the first column in the file, y is
the second column, σy is the third column,
σx0 is not
used.
Examples for two independent variables:
order 2 1 0 3 x0 is the third column in the file, x1 is the second column, y is the first column, σy is the third column.
order 1 4 2 x0 is the second column, x1 is the fifth column, y is the third column, σy is not specified.
order 0 1 2 3 4 5 x0 is the first column in the file, x1 is the second column, y is the third column, σy is the fourth, σx0 is in the fifth column and is used in the fit, σx1 is in the sixth column and is used in the fit.
order 0 1 2 3 -1 -1 x0 is the first column in the file, x1 is the second column, y is the third column, σy is the fourth, σx0 and σx1 are not used in the fit.