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Referring to literal row and column labels

In various MAT operations matrix rows and columns can be referred to
either by their numerical indices 1,2,... as in
MAT C=A(1:7,2:5)
or by symbolic expressions as in
m=7 k=1 n=5
MAT C=A(1:m,k+1,n).

It is also possible to use names of rows and columns literally
in such operations.
For example, if R is a correlation matrix of variables X1,X2,Y1,Y2,
MAT R3=R(X2:Y2,X2:Y2)
gives R3 as a correlation matrix of the three last variables X2,Y1,Y2 and
MAT LOAD R(*,Y1)
loads the third (Y1) column of R into the edit field.
Any reference to a row or to a column is in the first place interpreted
as a row (or column) label.
If this fails, it is handled as a symbolic expression or a plain index.
  M = More information on MAT operations