Defines required branch of spanning-tree
Connections.branch(A.R,B.R);
Defines a branch from the overdetermined type or record instance
R in connector instance A to the
corresponding overdetermined type or record instance R
in connector instance B for a virtual connection
graph. These branches are required to be part of the spanning-tree
for the virtual connection graph (they do not directly generate
equations, but should be combined with equations coupling
A.R to B.R), whereas connect-statements
are optional for the spanning-tree (and generate different
equations depending on whether they are part of the spanning-tree
or not).
This function can be used at all places where a connect(...) statement is allowed.
E.g., it is not allowed to use this function in a when-clause.
This definition shall be used if in a model with connectors
A and B the overdetermined records
A.R and B.R are algebraically coupled in
the model, e.g., due to B.R = f(A.R, <other
unknowns>).