thank you, Ken and Andrew for your kindly reply of the question "segmentation fault" posted by me. I will contact Cadence support team.
I have another question related to monte carlo simulation.
I have a circuit which has several control pins, e.g. S<2:0>. By changing the setting
of S<2:0>, I can change the performance of the circuit to cover P.V.T.( Process,
voltage and temperature) variation.
Now I am doing Monte Carlo simulation to check the performance of that circuit.
I set S<2:0> = 100, at Run #32, I fail to meet the spec. but if I change the setting
of S<2:0> to 101, maybe I can meet the spec. The problem is, if I change the setting
of S<2:0>, the Gaussian distribution of each devices of the circuit also change, so
Run #32 is not the same between setting S<2:0> = 100 and S<2:0> = 101, then I cannot know with S<2:0> = 101, under the failed condition, the circuit can work or not.
I am not a native English speaker. I don't know whether I have expressed my question clearly or not. If any confusion, please let me know.

Best Regards,
River

Is you input a kind of a trimming input which get programmed during wafer-test or so? This means that you have to simulatate the trimming process too. If your need help on this, let me know.
If S is a input in your device, the distribution of the random device parameters should not change.
- achim

Yeah, I believe during trimming process, the random device parameters will not change. but unfortunatly, I cannot do that trimming simulation, because it takes long time and monte carlo simulation is unrealistic. So now I want to check whether my control code S<2:0> is
enough or not to cover 3-sigma process variation. I believe the trimming process has no problem. As long as the control code S<2:0> can cover the process variation, the trimming process can calibrate the circuit to the correct working point.
I believe if I don't stop the simulation, the random device parameters will not change.
but only after simulation I can check the performance of the circuit, and then change the control code (say, change the voltage of a DC voltage source which is connected to the control code). With this new control code, I re-run the simulation and I want to check the performance of the circuit with previous device parameters. I think Run# is the seed for random device parameters generation, that means if Run# is the same, the device parameters should also be the same. That's true if I don't change the control code. The monte carlo simulations show that fact. But if I change the control code, even the seed is the same, but the device parameters are changed.
Finally, my question is how to attain the same device parameters with different control code settings?

Best Regards,
River

[quote author=river  link=1126140887/0#4 date=1126315839]
But if I change the control code, even the seed is the same, but the device parameters are changed.
[/quote]

This seems odd to me.  Unless the control code changes the topology of the circuit, it seems that the seed should give the same results for the parameters.  (If you had more devices in your circuit, then there would be more calls to the random number generator, and the values for devices encountered after the new devices would be different in the new run.)

you are right.
Changing those control signals will not alter the random device parameters.
I neglected the fact that vth is a function of vds(here, I mean vds, not vbs).
thank you for your help.

Best Regards,
river