External data can be plotted on any standard plot. The external data can be measurement results (measured beta-functions, differential orbits, etc.) or desired values for certain parameters. By comparing external data with model predictions one can attempt to interactively fit (use Edit|Increment and Edit|Decrement) the model to the data. This mechanism is often sufficient and while it cannot not replace more specialized programs it is of great help for preliminary data analysis when experimental uncertainties (like wrong sign of BPM measurement) can cloud the fitting results. To read data into a graphical window click the right mouse button in the top part of the window (see Graphical Window). That pops up a dialog box.
Each external data file is a plain text file with space or tabs separated columns. The length of every line should not exceed 255 characters. The dialog box allows one to chose columns for x and y coordinates, and, if necessary, for error bars. A Column number equal to zero implies that this column is not used. Therefor, if the index of at least one of two error-bar columns is zero, error bars will not be plotted. Lines starting with the character # are considered as comments and are ignored. There are two different methods to set the longitudinal coordinates of the plotted points.
If the check box Reference S coordinate to S0 is checked the initial path length (s-coordinate from the line 8 of OptiM file; see Input language description) is subtracted from the longitudinal coordinates kept in the file. This mechanism allows one to use the same data files for plotting data inside different short pieces of long machine.
Plotting of experimental data (or any other information) allows one to perform a wide range of machine studies. For example: the plotting of BPM measurements (or differential BPM measurements) inside Tools|Trajectory window allows one to understand errors in bending angles of dipoles (or focusing strength of quadrupoles) and determine required values for correctors (or quadrupole corrections); the plotting of beta-function measurements inside View|Betas window allows one to understand errors in focusing strength of quadrupoles. Similar procedure can be performed with other graphical windows. The use of Edit|Increment and Edit|Decrement commands allows interactively perform optics adjustments which accelerates finding out errors of machine optics.
External file example: # s[m] dx1[cm] dxm[cm] dxp[cm] name alarm -9620.2803 0.0000 0.0000 0.0000 IPM0L01 -9263.3896 -0.0001 -0.0028 0.0027 IPM0L02 -8673.1797 0.0000 0.0000 0.0000 IPM0L03 -8358.1797 0.0003 -0.0008 0.0013 IPM0L04 -7376.7598 0.0000 0.0000 0.0000 IPM0L05 ...