$PROBLEM    2 compartment fitting
$INPUT       ID TIME AMT DV WTKG GENDER AGE DROP
$DATA      {data_dir}/dataExample1.csv IGNORE=@
           
$SUBROUTINE ADVAN2
$ABBR DERIV2=NO
$PK      
  CWTKG = WTKG/70  ;; CENTERED ON ONE 
  CAGE = AGE/40
;; thetas out of sequence
  TVV2=THETA(2){V2~WT[1]} {V2~GENDER[1]}
  V2=TVV2*EXP(ETA(2)) 
  TVCL= THETA(1) {CL~WT[1]}  
  CL=TVCL*EXP(ETA(1)) 
  K=CL/V2  
  TVKA=THETA(3) 
  KA=TVKA  {KAETA[1]}  
  S2 	= V2/1000 
  {ALAG[1]}
$ERROR     
 REP = IREP      
 IPRED =F  
 IOBS = F {RESERR[1]}
 Y=IOBS
$THETA  ;; must be one THETA per line.
 (0.001,100)	; THETA(1) CL UNITS =  L/HR
 (0.001,500) 	; THETA(2) V  UNITS = L
 (0.001,2) 	; THETA(3) KA UNITS = 1/HR  
  
 {V2~WT[2]}   ;;; comment must consist of more than one word
 {V2~GENDER[2]}   ;;; otherwise it's a definition, and it will push you back
 {CL~WT[2]}  
 {ALAG[2]}
 
$OMEGA   ;; must be one ETA/line
  0.2  		; ETA(1) CLEARANCE
;; test for comments in blocks
  0.2  	; ETA(2) VOLUME
;; optional $OMEGA blocks
{KAETA[2]}   
  
$SIGMA   

{RESERR[2]} 
$EST METHOD=COND INTER MAX = 9999 MSFO=MSF1 
$COV UNCOND PRINT=E