Adds two files. The intensity of the second inputfile is multiplied by the scale and added to the intensity read from inputfile 1. Optionally the type of the inputfiles can be given. It defaults to "ni" for files in the standard format. type should be "gnu" for gnuplot files and "1d" for one-dimensional files.
For standard files, the respective headers are compared for consistency. for gnuplot and one dimensional files the h,k,l are compared line by line. If an error is detected, the procedure stops. Thus it is possible for the result files to be incomplete. They are not deleted to allow comparison with the input files.
Any one of the two input files may be identical to the result file, while the two input files must be different files.