Recasting Data Recasting Data

There are three special commands in this menu: SPECTRUM, FFT and CULL. All of these commands take a subset of the original data and transform it into a new set of data to be disposed. This has the interesting effect of one being in the Disposition Menu from the Disposition Menu. The first time and END is encountered, one leaves the latest Disposition Menu, but is still in the Disposition Menu. Now, however, the original data is again available.

There are several options which can be used on more than one command:


     -RECORD, BEG_RNUM, END_RNUM

     -VALUES, CV,  VAL_MIN, VAL_MAX
 

The -RECORD and -VALUES options defines the records which will be considered. Here, a "RECORD" is simply a row of the matrix of data. With the -RECORD option the beginning and end record numbers are simply specified. With -VALUES the records considered are defined with the values of a column of data. Here CV is the column number for which the values will be obtained and VAL_MIN and VAL_MAX are two numbers (VAL_MIN is less than VAL_MAX). BEG_REC is then the largest record number which the values of column CV is less than or equal VAL_MIN and END_REC is the greatest record number where the value of this column is greater than VAL_MAX. If neither -VALUES nor -RECORD are specified, all records will be considered.

The form of the first of these commands is:


     SPECTRUM, CS(1), CS(2), .....  -OPTIONS

and the available options are:


     -RECORD, BEG_RNUM, END_RNUM

     -VALUES, CV, VAL_MIN, VAL_MAX

When issued, MOSES will compute a spectrum for the columns selected by CS(2), .... CS(N), assuming that CS(1) is the independent variable. The form of the second one is:


     FFT, CS(1), CS(2), .....  -OPTIONS

and the available options are:


     -RECORD, BEG_RNUM, END_RNUM

     -VALUES, CV, VAL_MIN, VAL_MAX

These two commands are very similar, the only difference is that with FFT, a Fourier transform of the data is produced instead of a spectrum. The last of these special commands is:

     CULL, CS, EXL(1), EXU(1), ....  EXL(n), EXU(n)

This command creates a new set of data from the original by excluding specified parts. Here, CS defines a column, and other values define ranges of values of the selected column which will be excluded in the new data. For example, consider:

     CULL, 1, 0 50 200 300

The new data will contain all of the original except those rows where column 1 had values either between 0 and 50 or 200 and 300. One obvious use for this command is to extract starting transients from a time sample. Another use is to partition frequency domain data to compute independent statistics on each part.