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RE: Simulation problem of normal distributed data

From: Bauer, Robert <Robert.Bauer>
Date: Tue, 29 Jul 2014 22:53:11 +0000

Sheng:
This seems like a rather arbitrary occurrence. If you would supply me with your problem (control stream file and data set), I would be happy to determine if there is a bug. Please let me know what version of NONMEM you are using, compiler, and operating system.

Robert J. Bauer, Ph.D.
Vice President, Pharmacometrics, R&D
ICON Development Solutions
7740 Milestone Parkway
Suite 150
Hanover, MD 21076
Tel: (215) 616-6428
Mob: (925) 286-0769
Email: Robert.Bauer
Web: www.iconplc.com<http://www.iconplc.com/>

From: owner-nmusers musers
Sent: Tuesday, July 29, 2014 6:25 PM
To: Gerry Sheng
Cc: nmusers
Subject: Re: [NMusers] Simulation problem of normal distributed data

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) (17545 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
<br /><br />
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Received on Tue Jul 29 2014 - 18:53:11 EDT

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