c1: READ FILE=colvar.in VALUES=cv1
c2: READ FILE=colvar.in VALUES=cv2

ff: COLLECT_FRAMES ARG=c1,c2 
pca: PCA USE_OUTPUT_DATA_FROM=ff METRIC=EUCLIDEAN NLOW_DIM=2
dat: PROJECT_ALL_ANALYSIS_DATA USE_OUTPUT_DATA_FROM=ff PROJECTION=pca

OUTPUT_ANALYSIS_DATA_TO_COLVAR USE_OUTPUT_DATA_FROM=dat ARG=dat.* FILE=colvar FMT=%8.4f
