AUTORG is a command-line program to estimate the radius of gyration (Rg) using the well known Guinier approximation
I(s) = I(0)exp(s2Rg2/-3).
The value of Rg is estimated from the best possible linear fit of ln[I(s)] versuss2 (Guinier plot), which is valid for sufficiently small scattering vectors (in the range up to sRg ≤ 1.0–1.3). The radius of gyration provides an estimate of the overall size of a particle (the root mean square distance to center-of-mass in a particle). Linearity of the Guinier plot is a sensitive indicator of the quality of the experimental data, and deviations from linearity usually point to strong interference effects, polydispersity of the sample or improper background subtraction. Based on that the program also estimates the quality of the input data. Please refer to the paper cited above for further details about the implemented algorithm.
Output format, one of: csv, ssv, table.
'csv' will force to produce the output in Excel-compatible comma separated values format, a header will be written.
'ssv' will force to produce the output in machine-readable space separated format without a header; the sequence of values is same as in CSV format apart from the file name – it will be written last, not first.
'table' will force to produce the output as a human-readable table with round values. This is the default value if more than one input file is given.
AUTORG accepts SAS experimental data files (*.dat) in ASCII format containing 3 columns: (1) momentum transfer, (2) experimental intensity and (3) experimental errors. If errors are not present, they are estimated as 4% of the intensity.
AUTORG prints the result to standard output unless the output option was specified.
AUTORG output includes:
Estimated radius of gyration. If the input data was in Å-1 the unit of Rg is Å; if the input data was in nm-1 the unit of Rg is nm.
Standard deviation of the experimental data from the Guinier fit in the selected interval plus standard deviation of Rg values from all possible intervals from the Rg value from the selected interval. This way the accuracy of Rg is estimated by taking into account not only the error propagation in the selected fit but also by accounting for the deviation of Rg values calculated from other consistent intervals, accounting to some extent for systematic errors in the Rg determination.
Extrapolated scattering intensity at zero angle I(0) (forward scattering).
Standard deviation of the I(0) value. Please note that this value is estimated only from the selected interval and therefore is underestimated.
First point of the Guinier interval. Counting of data points starts from 1. Data points before the first point should not be used in further data processing.
Last point of the Guinier interval. In table format total number of points is given in brackets.
Estimated data quality. 1.0 – means ideal quality, 0.0 – unusable data. In table format it is given in percent (100% – ideal quality, 0% – unusable data). Please note that this estimation is based only on the Guinier interval (very low angles) and the number of negative intensities.
A number between -1.0 and 1.0 expressing the trend of the data before the chosen Guinier interval. Positive values indicate possible aggregation or background subtraction problems; negative values indicate repulsive interactions or background subtraction problems; values close to zero indicate good data quality.