The determination of specific placement of the geometric elements in a generic solver takes place only after a decision has been made about whether or not the problem is generically well-constrained. As an example of the two different approaches, consider the sketch of Figure 1. Here the constraints are given symbolically, rather than with actual values. A generic solver would be able to report that the configuration is well-constrained , and would be able to determine a method for constructing the possible configurations without needing the actual values of the constraints. An instance solver requires that the values of the constraints be given before it makes any solution determination.
Generic solvers are often more elegant and more efficient than instance solvers.
They also allow more flexibility in the choice of the underlying method applied to determine the actual positions of the geometric elements. However, generic solvers usually are not able to handle the case of overconstrained but consistent systems, while most instance solvers can find the solution. A well-constrained sketch may yield fundamentally different solutions. This means that a well-constrained profile may have an exponential number of distinct solutions, dependent on the number of geometric elements. For example, Figure 2 shows three possible solutions of a well-constrained profile that differ in the interpretation of the function of the arc, the tangency type, and the right angle constraint between two segments.