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#1 Shu-Pei Wu

Shu-Pei Wu

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Posted 06 August 2014 - 07:58 PM

Hi Pharsight Modellers,

 

I have question regarding to the calculation of condition number in phoenix.

In the user guide, it states that when the condition number exceeds 1E+6, then the model is probably overparameterized.

 

However, I recalled that when using NONMEM, the criteria is <1000, (it happens to be square root of 1E+6).

 

I wonder how the difference just because the calculation?

 

Thanks,

Shu-Pei



#2 Simon Davis

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Posted 07 August 2014 - 11:40 AM

Shu-Pei, as I understand the condition number is a property of the actual problem so as a general rule of thumb, if the condition number is less than = 10^number of parameters then it is probably well-conditioned.

 

  However I've seen it exceed this and still been a good fit by other metrics so I wouldn't look at it in isolation.

 

  Simon



#3 Shu-Pei Wu

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Posted 07 August 2014 - 02:54 PM

Hi, Simon,

 

Thanks for your response for sharing the general rule of thumb of looking at condition number.

I also agree that it is just one of many diagnostic indicators for accessing the model.\

 

Thanks again,

Best,

 

Shu-Pei






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