Syntax:

-SYSREM Ninput_color Ninput_airmass initial_airmass_file sigma_clip1 sigma_clip2 saturation correctlc omodel [model_outdir] otrends [trend_outfile] useweights

Example 1.
$ ./vartools -l EXAMPLES/trendlist_tfa -header \
    -rms \
    -SYSREM 2 1 EXAMPLES/3 5. 5. 8. 1 \
        1 EXAMPLES/OUTDIR1 1 EXAMPLES/OUTDIR1/sysrem.trends 1 \
    -rms

#Name Mean_Mag_0 RMS_0 Expected_RMS_0 Npoints_0 \
    SYSREM_MeanMag_1 SYSREM_Trend_0_Coeff_1 SYSREM_Trend_1_Coeff_1 SYSREM_Trend_2_Coeff_1 SYSREM_RMS_1 \
    Mean_Mag_2 RMS_2 Expected_RMS_2 Npoints_2
EXAMPLES/4  10.35142   0.00209   0.00114  3227  \
    10.35130  -0.83218  -0.86967  -0.03662   0.00087  \
    10.35137   0.00116   0.00114  3227
EXAMPLES/5  10.43962   0.00288   0.00114  3903  \
    10.43976  -0.03154  -0.05758  -0.02459   0.00177  \
    10.43962   0.00197   0.00114  3903
EXAMPLES/6  10.52762   0.00209   0.00121  3933  \
    10.52774   0.28190   0.30516   0.02490   0.00104  \
    10.52762   0.00115   0.00121  3933
EXAMPLES/7  10.56966   0.00349   0.00116  3626  \
    10.56988   0.14423   0.11560  -0.02852   0.00239  \
    10.56969   0.00254   0.00116  3626
EXAMPLES/8  10.61152   0.00225   0.00125  3957  \
    10.61160   0.01083   0.00955   0.00017   0.00178  \
    10.61152   0.00181   0.00125  3957
EXAMPLES/9  10.73139   0.00187   0.00133  3954  \
    10.73148   0.14601   0.13900  -0.00614   0.00124  \
    10.73139   0.00142   0.00133  3954
EXAMPLES/10  10.87781   0.00236   0.00143  3974  \
    10.87792   0.23422   0.25903   0.02672   0.00105  \
    10.87781   0.00120   0.00143  3974

Example illustrating the syntax of the -SYSREM command. We apply SYSREM to the light curves in the list EXAMPLES/trendlist_tfa, using 2 initial "color"-like terms (corresponding to the second and third columns in EXAMPLES/trendlist_tfa) and one initial "airmass"-like term. For the "airmass"-like term was use the file EXAMPLES/3. We apply 5 sigma-clipping for determining the mean magnitudes of the light curves and for determining whether or not points contribute to the iterative SYSREM fit. We set the saturation magnitude to 8.0 and we correct the light curves. We output the SYSREM model light curves to the directory EXAMPLES/OUTDIR1 and we output the trends to the file EXAMPLES/OUTDIR1/sysrem.trends. We caluclate the RMS before and after applying -SYSREM to illustrate the effect of SYSREM on the light curves. In practice one would apply SYSREM to a much larger set of light curves, and would use the airmass, seeing, temperature and other known image-dependent parameters (i.e. parameters which differ from image to image, but are fixed for all stars in a given image) for the initial "airmass"-like terms, and parameters such as the ra/dec, star colors, and other known star-dependent parameters (i.e. parameters which differ from star to star, but are fixed for a given star over all images) for the initial "color"-like terms.