SOM Toolbox Online documentation http://www.cis.hut.fi/projects/somtoolbox/

# sammon

P = sammon(D, P, varargin)

```SAMMON Computes Sammon's mapping of a data set.

P = sammon(D, P, [value], [mode], [alpha], [Mdist])

P = sammon(D,2);            % projection to 2-dim space
P = sammon(sMap,3);         % projects the codebook vectors
P = sammon(sMap,3,[],[],[],Md) % uses distance matrix Md
som_grid(sMap,'Coord',P)    % visualization of map projection

Input and output arguments ([]'s are optional):
D        (matrix) size dlen x dim, data to be projected
(struct) data or map struct
P        (scalar) output dimension
(matrix) size dlen x odim, initial projection matrix
[value]  (scalar) all different modes (the next argument) require
a value, default = 100
[mode]   (string) 'steps' or 'errlimit' or 'errchange' or 'seconds',
see below, default is 'steps'
[alpha]  (scalar) iteration step size, default = 0.2
[Dist]   (matrix) pairwise distance matrix, size dlen x dlen.
If the distances in the input space should
be calculated otherwise than as euclidian
distances, the distance from each vector
to each other vector can be given here,
size dlen x dlen. For example PDIST
function can be used to calculate the
distances: Dist = squareform(pdist(D,'mahal'));

P        (matrix) size dlen x odim, the projections

The output dimension must be 2 or higher but (naturally) lower
than data set dimension.

The mode argument determines the end condition for iteration. If
the mode argument is used, also the value argument has to be
specified. Different mode possibilities are:
'steps'      the iteration is terminated when it is run
'errlimit'   steps, the iteration is terminated when projection error
is lower than ,
'errchange'  the iteration is terminated when change between
projection error on two successive iteration rounds
is less than  percent of total error, and
'seconds'    the iteration is terminated after  seconds
of iteration.