MEANCOV 1A 02 April 2001 NIST NFIS Reference Manual meancov computes mean vector and covariance matrix for a set of feature vectors. meancov <vecsfile_in vecsfile_in > <meanfile_out><meanfile_out_desc><covfile_out><covfile_out_desc><ascii_outfiles><message_freq> Meancov computes sample mean vector and sample covariance matrix of a set of feature vectors. If several processors are available, it may be possible to save time, when computing the mean and covariance of a large set of feature vectors. First, run several simultaneous instances of meancov, each instance computing the mean and covariance of a subset of the vectors. Then, use cmbmcs to combine the resulting output files. See the cmbmcs man page. Note: If using cmbmcs, the subset mean vectors made by the meancov instances must be saved for later use by cmbmcs even if, ultimately, all that is wanted is the overall covariance matrix. Construction of the overall covariance requires the subset means, as well as the subset covariances. <vecsfile_in[vecsfile_in...]> Input data file(s) in PCASYS "matrix" format, each consisting of a block of the vectors that are to be used, i.e. the vectors are the rows of the matrix (matrices). Of course, all input matrices must have the same second dimension, which is the dimension of the constituent vectors. (Usually the output of mkoas.) <meanfile_out> Mean file to be written, in PCASYS "matrix" format, with first dimension set to 1 and with second dimension set to the dimension of the input vectors. <meanfile_out_desc> A string to be written into the mean output file as its description string. This string can be of any length, but must not contain embedded newline characters. If it contains spaces, tabs, or shell metacharacters that are not to be expanded, then it should be quoted. To leave the description empty, use '' (two single quotes, i.e. single-quoted empty string). To let meancov make a description (stating that this is a mean vector made by meancov and listing the names of the input files), use - (hyphen). <covfile_out> Covariance file to be written. Meancov saves memory and cycles by allocating a buffer only large enough for the nonstrict lower triangle of the symmetric covariance matrix and computing only those elements, and it saves disk space by storing the covariance in PCASYS "covariance" format, which stores only the nonstrict lower triangle. The order of the covariance is the dimension of the input vectors. <covfile_out_desc> Description string for covariance file or - to let meancov make the description, same as for the mean file description argument. <ascii_outfiles> If y, makes ascii output files; if n, binary. Binary is recommended, unless the output files must be portable across different byte orders or floating-point formats. <message_freq> If a positive integer, then every this many vectors through each input file, during the accumulation phase, meancov writes a progress message to the standard output, and it also writes a few other progress messages. If 0, no messages. From test/pcasys/execs/meancov/meancov.src: % meancov ../../data/oas/fv[1-9].oas fv1-9.men - fv1-9.cov - n 100 Compute the mean and covariance matrices for a set of feature vectors. cmbmcs (1), mkoas (1) NIST/ITL/DIV894/Image Group