The results of a motion analysis are calculated during the solving process. This is a complicated process whereby a set of coupled Differential and Algebraic Equations (DAE) defines the equations of motion of a SOLIDWORKS Motion model.

A solution of these equations is obtained by integrating differential equations along with satisfying algebraic constraint equations at each step. The speed of the solution depends upon the numerical stiffness of these equations; the stiffer the equations, the slower the solution.

Special efficient integration methods are required to solve numerically differential equations; because the usual methods for solving differential equations perform poorly and are too slow. The SOLIDWORKS Motion solver offers three integration methods for computing motion. Each of these integrators are best used in specific situations but may not work well if used to solve the wrong type of simulation.

**GSTIFF**

Advantages:

- It is a variable order and variable step size integration method.
- It is the default method used by SOLIDWORKS Motion solver.
- It uses backward difference formulation.
- It is a fast and accurate method for computing displacements over wide range of application.
- The coefficients used internally by GSTIFF are calculated assuming a constant step size.

Disadvantages:

- GSTIFF introduces a small error in the solution.

**WSTIFF**

Advantages:

- In it a variable order and variable step size integrator method.
- It is similar to GSTIFF in formulation and behavior.
- It uses backward difference formulation.
- The coefficients used internally by WSTIFF are function of STEP function.
- It gives solution without loss of accuracy.
- The problems run more smoothly in this method.

Disadvantages:

- A sudden change in step size occurs whenever there are discontinuous forces, discontinuous motions, or abrupt events, such as 3D contact in the model.

**Stabilized Index 2 (SI2)**

Advantages:

- It is a modification of GSTIFF integration method.
- It provides better error control over velocity and acceleration terms in motion equation.
- It gives accurate results for velocity and acceleration (if provided motion is sufficiently smooth).
- It gives accurate results for high frequency oscillation (if provided motion is sufficiently smooth).
- It is more accurate with smaller step size.

Disadvantages:

- It is significantly slower for smaller step size.