NONMEM Users Network Archive

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Re: Simulation problem of normal distributed data

From: Gerry Sheng <shengyc>
Date: Wed, 30 Jul 2014 09:40:16 +0100

Dear Goyal,

Thank you for your advice. I changed the second seed to 17545, but the new
cutoff number of records is 1498 . If data records>1498, the same problem
still exists.

Best wishes,
Yucheng Sheng
Research Associate
School of Pharmacy, UCL


On 29 July 2014 23:25, Navin Goyal <navingoyal

> Hi Sheng,
> I don't know the exact reason behind such mysterious behavior but if you
> just change the seed number (the UNIFORM seed) it works.
> e.g. I changed the seed# from 7545 to 17545 and was able to simulate
> 1000 rows for the subject.
>
> $SIMULATION (6446) (*1*7545 UNIFORM) ONLYSIM NOPRED SUB=1
>
> Its a rare occurrence but may be the seed number caused some issue (while
> generating sufficient samples to satisfy the constraints you set up using
> the DOWHILE LOOP). For example I think the same seed number (7545) may
> work when the DOWHILE condition is reversed
> (RL .*LT*. PRN) however it may not be appropriate based on your problem.
> .......or may be there is some other explanation to such occurrence.
>
> Kind regards
> Navin Goyal
>
>
>
>
>
>
> On Tue, Jul 29, 2014 at 10:54 AM, Gerry Sheng <shengyc
>
>> Dear NMuser,
>>
>> I encountered a strange problem when I used the following code to
>> simulate normal distributed data. When the data records >797, no result
>> appears with NONMEM run into an infinite loop . But when the records
>> decreasing to 796 (delete the last row), the results will occurred
>> immediately. Anyone else met this phenomenon? Any comments and suggestions
>> are appreciated. Thank you in advance.
>>
>> $PROBLEM PD
>> $INPUT ID,CONC,DV
>> $DATA data.csv IGNORE=
>>
>> $PRED
>> NMEAN=THETA(1)+ETA(1)
>> SD=THETA(2)
>>
>> ;Simulate count
>> IF (ICALL.EQ.4) THEN
>> N=0
>> PRN=0
>> CALL RANDOM(2, R)
>> RL=1-R
>> DO WHILE (RL .GT. PRN)
>> LNNOR=LOG(6.283185)+2*LOG(SD)+((N-NMEAN)/SD)**2
>> PY=EXP(-0.5*LNNOR)
>> PRN=PRN+PY
>> IF (PRN .LT. RL) N=N+1
>> ENDDO
>> DV=N
>> ENDIF
>>
>> $THETA
>> (30,41.7,60) ;MEAN
>> (2,14.4,50) ;SD
>>
>> $OMEGA
>> 0 FIX ;MEAN
>>
>> $SIMULATION (6446) (7545 UNIFORM) ONLYSIM NOPRED SUB=1
>> $TABLE ID TIME DV ONEHEADER NOPRINT FILE=npctab1.dta
>>
>> data.csv like this
>> ID CONC DV
>> 1 0 .
>> 1 0 .
>> 1 0 .
>> 1 0 .
>> 1 0 .
>> 1 0.01 .
>> 1 0.01 .
>> 1 0.01 .
>> 1 0.01 .
>> 1 0.01 .
>> .....
>>
>> Yucheng Sheng
>>
>> Research Associate
>> School of Pharmacy, UCL
>>
>
>
>
> --
> Navin Goyal
>

Received on Wed Jul 30 2014 - 04:40:16 EDT

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