Demo 1 – standard test on robustness

Demo 1 – standard test on robustness

Let’s switch off Cheetah solver and load file Demo1_Ac.dwg from the folder Demo1 – Six Circles Inside Angle (it is the subfolder of the Cheetah.Solver).

In this model (with standard AutoCAD constraints) you have an angle with six circles. These 8 entities (six circles and two line segments) are connected by 15 tangent constraints and one coincident constraint.

This is the classical test on robustness of constraints solver. The term “robustness” means that, if you change “a little” any parameter of the constrained model, then the whole constrained model should change “a little” as well.

Six circles and two line segments with tangent constraints

Let’s drag a little the angle point (bottom left corner on the image below):

Drag a little the angle point – one circle becomes very big

We can see that after a small drag of the angle point the radius of one of the circles became very big. This is the typical example of the non-robust behavior of the solver.

Now let’s switch from the AutoCAD mode to Cheetah mode (see section 5.1). If you didn’t close the file Demo1_Ac.dwg yet, then AutoCAD constraints of this file will be converted to the Cheetah constraints:

The same model as in Fig.20, but with Cheetah constraints

Now let’s drag the angle point in the same way as we did it in AutoCAD mode:

Drag a little the angle point – the whole model changes a little

You can see a very robust behavior of Cheetah solver – a little drag of the angle point results in very little changes (blue lines) of the whole model.



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