Syntax
BD>fvar : v(S, X [IL
where S is a belief store number, X and Y are the names of
components or elements,
The FVAR: command is used to specify variances and covariances
functionally for components and between components and elements. At
least one of X and Y should be a component, but one may be an
element. The functional belief being defined is expressly limited to belief
store number S, and will overwrite any functional belief expressed for
the same pair of quantities for the same belief store. However, further
functional beliefs could be expressed about the same pair of quantities
for different belief store numbers.
The index list comprises single alphabetic characters, preceded by
the `.' symbol. An alphabetic character must not appear more than once
in the entire naming part, and the number of indices per component is
currently limited to 8.
The equation E will usually relate to the as yet unknown indices of
the naming part. As an example, consider the quantities
BD>fvar : v(1,eta.i,eta.j)=(.i=.j)+(.i<>.j)/(.i+.j)
], Y [IL 
]) = E 
are index lists, and
E is an equation, possibly involving indices from either index list.
discussed in (6.1) above, and suppose that we wish to specify
the variance-covariance structure for belief store number 1 for these
quantities. We could use the following command to achieve this: