inverse gaussian input function

Dear NMUsers, I need new pairs of eyes to look at the small problem I'm facing. The solution is probably right before my nose but I can't seem to get a hold of it. Let me explain briefly, I wrote two small test control files (pasted below), one for a weibull input function (inspired from http://www.cognigencorp.com/nonmem/current/2010-April/2476.html) and the other for an inverse gaussian input function. Note that In the $DES, block I only put the weibull or inverse gaussian and no clearance related parameters so I should end up with a cumulative distribution of the input function. The thing is this, it works just fine for the weibull with the function cumulating to one but I cannot seem to get it to work for the inverse gaussian. The shape of the inverse gaussian cumulative distribution is OK, it's the scale that's the problem, the cumulated input does not add up to one but to much less (to 0.397,actually). I figured it's probably just an error in my coding of the inverse gaussian pdf but having scrutinized it so much I just don't see it anymore. Below are my two control streams. If you build a dataset to run with the code be sure to put a lot of timepoints between 0 and 1 because the MAT parameter of the inverse gaussian is small (immediate release formulation). Thanks for your help :o) 1) Weibull ---------------------------- $PROBLEM WEIBULL INPUT FUNCTION SIM, SINGLE SUBJ $INPUT C ID AMT TIME DV MDV EVID $DATA DESTEST.CSV IGNORE=C $SUBROUTINE ADVAN6 TOL=3 $MODEL NCOMP=1 COMP=(CENTRAL) $PK F1=0 BETA=THETA(1) ALPHA=THETA(2) $DES ; WEIBULL FUNCTION PDF WB=(BETA/ALPHA)*((T/ALPHA)**(BETA-1))*EXP(-(T/ALPHA)**BETA) DADT(1)=WB $THETA 4.10 ;BETA 3.09 ;ALPHA $OMEGA (FIX,0) $ERROR Y=F+ERR(1) $SIMULATION (234134) ONLYSIM $TABLE TIME Y NOPRINT FILE=WB.TAB $SCATTER Y VS TIME ---------------------------- 2) Inverse gaussian ---------------------------- $PROBLEM INVERSE GAUSSIAN SIM, SINGLE SUBJ $INPUT C ID AMT TIME DV MDV EVID $DATA DESTEST.CSV IGNORE=C $SUBROUTINE ADVAN6 TOL=3 $MODEL NCOMP=1 COMP=(CENTRAL) $PK F1=0 MAT=THETA(1) CV=THETA(2) CV2=CV**2 $DES ;INVERSE GAUSSIAN PDF P1=2*3.141593*CV2*TIME**3 P2=(TIME-MAT)**2 P3=2*CV2*MAT*TIME P4=SQRT(MAT/P1) RATIO=-1*(P2/P3) P5=EXP(RATIO) IG=P4*P5 DADT(1)=IG $THETA 0.062 ;MAT 0.466 ;CV $OMEGA (FIX,0) $ERROR Y=F+ERR(1) $SIMULATION (323454) ONLYSIM $TABLE TIME Y NOPRINT FILE=IGTEST.TAB $SCATTER Y VS TIME ---------------------------- Pierre-Olivier Tremblay