*SetSolverVariable() - single solver variable with user subroutine
Sets the properties of a solver variable with a user subroutine.
Syntax
*SetSolverVariable(sv_name, USER, `solver_expression`) 
*Set(sv_name.use_local_dll, TRUE|FALSE) 
*Set(sv_name.local_dll, "string")
    Arguments
- sv_name
 - The variable name of the solver variable.
 - USER
 - Indicates that a user subroutine is used to compute solver variable properties.
 - solver_expression
 - A solver expression enclosed in back quotes to specify arguments for the user subroutine.
 - sv_name.use_local_dll
 - Specifies if a user subroutine DLL is specific to the instance of one solver variable entity.
 - sv_name.local_dll
 - The path and filename for the user subroutine DLL to be used with an instance of the user defined solver variable.
 
Example
*SolverVariable(sv_solvervariable, "Solver Variable" )
*SetSolverVariable(sv_solvervariable, 
 `7*DZ(marker1.id, marker2.id, marker2.id)`)
    Context
Comments
The solver variable is generally used to define a variable that is an algebraic function of solver parameters. This solver variable can then be referenced by other solver variables or passed into a user subroutine.