visualize_data

 Project high dim. data unto principal components (PCA) for visualization.

 Optionally IDX can be specified to indicate different classes for the points;
 in this case points in different classes are displayed using different colors.
 Up to 12 types are handled (for technical reasons involving plot), any 
 cluster with a label>12 is assigned the label 12.

 INPUTS
   X       - column vector of data - N vectors of dimension p (X is Nxp)
   k       - dimension to which to reduce data (2 or 3)
   IDX     - [optional] cluster membership [see kmeans2.m]
   types   - [optional] cell array of length ntypes of text labels for each type 

 EXAMPLE
   X=[randn(100,5); randn(100,5)+4];
   IDX=[ones(100,1); 2*ones(100,1)];
   visualize_data( X, 2, IDX, {'type1','type2' });

 DATESTAMP
   29-Nov-2005  2:00pm

 See also KMEANS2