The MDS Procedure

The INITIAL= data set has the same structure as the OUT= data set but is not required to have all of the variables or observations that appear in the OUT= data set. You can use an OUT= data set previously created by PROC MDS (without the OUTITER option) as an INITIAL= data set in a subsequent invocation of the procedure.

The only variables that are required are Dim1, ..., Dimm (where m is the maximum number of dimensions) or equivalent variables specified in the INVAR statement. If these are the only variables, then all the observations are assumed to contain coordinates of the configuration; you cannot read dimension coefficients or transformation parameters.

To read initial values for the dimension coefficients or transformation parameters, the INITIAL= data set must contain the _TYPE_ variable and either the variable specified in the ID statement or, if no ID statement is used, the variable _NAME_. In addition, if there is more than one data matrix, either the variable specified in the MATRIX statement or, if no MATRIX statement is used, the variable _MATRIX_ or _MATNUM_ is required.

If the INITIAL= data set contains the variable _DIMENS_, initial values are obtained from observations with the corresponding number of dimensions. If there is no _DIMENS_ variable, the same observations are used for each number of dimensions analyzed.

If you want PROC MDS to read initial values from some but not all of the observations in the INITIAL= data set, use the WHERE= data set option to select the desired observations.