Constraint
2D/3D• Constraint[cnum, equation, {bnum, ... }, {{extravar, guess}, ... } returns a SysCon data object that is used to add a user-defined constraint equation to a Mech model. The equation can be a single equation or a list of equations, each of which must have the head Equal. After creation, the SysCon object is passed to SetConstraints to alter the state of the current Mech model.
• The bnumi are an optional list of the body numbers of those bodies that are constrained by the equation.
• {extravar, guess} (or {{extravar, guess}, ... } ) is an optional list of symbols that appear in the model (and their associated initial guesses), that are added to the model's dependent variable list and solved for. • This function is used to enter constraints directly as equations when the desired relation is not attainable with the standard Mech mechanical constraints.
• The list of body numbers, {bnum, ... } can be omitted if the same bodies are also constrained by other system constraints.
• An {extravar, guess} pair associated with a particular extravar may appear in only one constraint in a model. The same extravar in more than one constraint will generate an error in SetConstraints.
• See also: Body, GenConstraint, Load. Further Examples Load the Modeler2D package and define a simple model. The help model was defined with OriginLock1 and RotationLock1 constraints for the crank body, which resulted in the following constraint expressions.
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Exactly the same state can be achieved by defining the constraint expressions explicitly.
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Because the constraint was defined so that body bdcrank would be added to the model, it is possible to use functions like Location or MassMatrix that require a body number.
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However, if the constraint was defined without adding a body to the model, instead treating X2, Y2, and  2 as completely independent variables, then all of the features and functions associated with having a body are not available.
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See HelpModel2D.
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