Re: Change of NSIG or R matrix
Dear Nick,
Thank you very much for your suggestion. Could you explain a little bit
about the statement regarding NSIG < 3? I seem to remember that many
suggested to use a smaller NSIG to get a successful minimization.
Dear Leonid,
I read about the recommendation of SIGL, NSIG and TOL, but I am not quite
familiar with the use of these options in subroutine ADVAN4. If I set SIGL
a fixed value, let's say 12, and NSIG 3, does this mean I also have to
identify a value for TOL in $subroutine? I appreciate your help very much.
Thank you both.
Regards
Quoted reply history
On 8 October 2013 21:59, Leonid Gibiansky <[email protected]> wrote:
> Yes, it should be fine to use S matrix if you cannot get default to run,
> and use NSIG larger or smaller than default value of 3 (although this is
> not guaranteed, usually NSIG does not change the OF value or parameter
> estimates in any significant way). Note that Nonmem manual recommends that
> SIGL >= 3*NSIG, TOL >= SIGL. Separate SIGL can be set on COV step, and it
> is recommended that SIGL >= 4*NSIG on COV step. In real life I've seen many
> examples where larger NSIG and SIGL resulted in successful COV step, and
> also many examples when default values were better (in getting COV step).
> UNCONDITIONAL on COV step allows you to run COV even when minimization
> ended with some error.
>
> Contrary to Nick's experience, I found that COV step is useful as it
> reveals which of the model parameters are poorly estimated, and that CI
> based on SE are usually quite good and are in a general agreement with the
> bootstrap CI, but it may depend on the problem.
>
> Leonid
>
>
> ------------------------------**--------
> Leonid Gibiansky, Ph.D.
> President, QuantPharm LLC
> web: www.quantpharm.com
> e-mail: LGibiansky at quantpharm.com
> tel: (301) 767 5566
>
>
>
>
> On 10/8/2013 3:57 AM, Xinting Wang wrote:
>
>> Dear all,
>>
>> I have a naive question regarding the modeling building process in
>> NONMEM. With more and more covariates added in the model, I often come
>> across an error message saying that "ERROR 134", or R MATRIX SINGULAR.
>>
>> After searching from the internet, I learned that changing NSIG in
>> $ESTIMATION and MATRIX=S in $COV would be helpful for both problems
>> respectively. And from my own experience, it dose help with the modeling
>> building.
>>
>> However, my concern is, I used different NSIG and MATRIX in the previous
>> steps. Is it proper to use different NSIGs and MATRICE in a single model
>> building? If not, could you please explain this a little bit?
>>
>> Thank you in advance!
>>
>> Best Regards
>> --
>> Xinting
>> Wang
>>
>>
--
Xinting