INITIAL Subcommand (PROXSCAL command)

INITIAL defines the initial or starting configuration of the common space for the analysis. When a reduction in dimensionality is specified on the CRITERIA subcommand, a derivation of coordinates in the higher dimensionality is used as a starting configuration in the lower dimensionality.

  • You can specify one of the three keywords listed below.
  • You can specify a variable list containing the initial configuration.

SIMPLEX. Simplex start. This specification is the default. PROXSCAL starts by placing the objects in the configuration all at the same distance of each other and taking one iteration to improve this high-dimensional configuration, followed by a dimension-reduction operation to obtain the user-provided maximum dimensionality specified in the CRITERIA subcommand with the keyword DIMENSIONS.

TORGERSON. Torgerson start. A classical scaling solution is used as initial configuration.

RANDOM. (Multiple) random start. You can specify the number of random starts (n). n is any positive integer. The random sequence can be controlled by the RANDOM SEED command and not by a subcommand within the PROXSCAL command. Each analysis starts with a different random configuration. In the output, all n final stress values are reported, as well as the initial seeds of each analysis (for reproduction purposes), followed by the full output of the analysis with the lowest stress value. The default number of random starts is 1. Reduction of dimensionality—that is, using a maximum dimensionality that is larger than the minimum dimensionality—is not allowed within this option and the minimum dimensionality is used, if reduction is specified anyway.

Instead of these keywords, a parenthesized IBM® SPSS® Statistics data file can be specified containing the coordinates of the initial configuration. If the variable list is omitted, the first MAXDIM variables are automatically selected, where MAXDIM is the maximum number of dimensions requested for the analysis on the CRITERIA subcommand. Only nonmissing values are allowed as initial coordinates.

Example 

PROXSCAL object01 TO object17 
  /INITIAL=RANDOM(100).
  • This example performs 100 analyses each, starting with different random configurations. The results of the analysis with the lowest final stress are displayed in the output.