Maxwell's Dream Help: How do I control the calculation? | Back to Overview |

The calculation is started with a push of a button:

During the calculation a process bar is active. The calculation can be stopped by pressing the button again.- The graphic of the calculated field is shown
- The calculated result values are shown
- The calculation monitor values are shown

At the beginning of the calculation the calculated fields and results are far away from being the correct solution. But with every iteration of the calculation the results are getting better and better. The calculation ends, when a certain level of accuracy is reached.

In the colored graphic not the field strength, but the electrical potential is shown.

It is assumed, that the ground planes have a potential of zero Volts. The signal trace has a high potential. The area between the signal trace and the ground planes has some potential value inbetween.

Red | Highest Voltage |

Yellow | High Voltage |

Green | Low Voltage |

Blue | Lowest Voltage |

You find the Calculation Monitor in the upper right part of the window:

The first value is the actual **size** of the finite elements array. This value is chosen automatically for you.

The second value is the number of **iterations** processed. For informational purposes only.

The third value is the elapsed **time**. You may want to look at this value, if you compare the speed of different Macintosh models.

The fourth value **QS / QM** is a criteria for the remaining errors of the iteration step. This value is used to end the iteration. To understand this value, you have to be aware, that avery electrical field in the surrounding of a metallic conductor induces some electrical charge at the surface of this conductor.

Q_{S} is the induced charge at the surface of the signal trace. Q_{M} is the induced charge at the surface of both ground planes. In the real world, these charges are balanced, which means that Q_{S} and Q_{M} have exactly the same value.

In the world of our calculation, in the beginning of the iteration the charges are not balanced at all. To be honest, Q_{S} is very large and Q_{M} is zero. Of course this is far away from a correct result. But the good news is, that with every iteration step the finite elements array is getting more and more similiar to the real world. The program Maxwell's Dream monitors this "similiarity" by looking at the ratio of Q_{S} and Q_{M}. If this ratio is equal to -1, the result is perfect. As you can see, the snapshot shown above is somewhere in the beginning of a iteration. The snapshot below is taken after the completion of an iteration:

The fifth value **QM / QB** is not used to terminate the iteration. It is a proof, whether the calculation in a bounded area has the same result as you would expect from the unlimited and unbounded area of a real triplate. You can find more on this topic in the chapter Tell me about the accuracy!

Of course there is a trade-off between calculation speed and accuracy. In the optimization menu you can choose between three modes:

You may use the **Coarse Accuracy**, if you want very fast results and an accuracy of about 10% is acceptable. A good example for the Coarse mode is the search for a geometry with an wave impedance in the desired range.

The **Normal Accuracy** is best used to define the exact geometric parameters for the desired wave impedance.

You can use **Fine Accuracy**, if you want to verify the results from the Normal Accuray or if you just want to give some work to your new high speed Mac. Be aware, that calculation with Fine Accuracy may take some time on older Macs.

With the default settings the programs enables the usage of an **AltiVec** unit, whenever such a unit is available. In the optimization menu you can disable the usage of AltiVec. The single purpose of this option is to see, how useful an AltiVec unit is. For finite elements analysis you can expect a speed bump factor of 2...3 by using the AltiVec unit. Test it yourself.

How do I define the geometry? | Back to Overview | Tell me about the accuracy! |

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