Problems of asymmetry

 

The beliefs that you specify over pairs and so forth must be symmetric: that is, for all X,Y we must specify . An illustration of the kind of problem that might arise is given below.

BD>element : a,b,c,d,e,f

BD>base : x=a,c,d,e

BD>base : y=b,c,d,f

BD>var : v(2,x,y)

BD*-2 -1 -1 -6

BD*-1 0 6 -5

BD*-1 5 0 -5

BD*-6 -5 -5 -6

This sequence of commands specifies a covariance matrix between the collections x and y. However, x and y are not disjoint - they both contain the elements c and d - and the actual specification mistakenly attempts to define and . An error is flagged whenever this kind of mistake occurs. This problem can arise also when using the VARDATA:  and MATMULT:  commands.