M3 method for LLOQ

$ERROR
; LLOQ values in the dataset should be set to 0
; a column FLG identifies the LLOQ rows
; FLG=1 for BQL and 0 otherwise
; MDV and EVID should be =0 for LLOQ rows

IPRED=F
LOQ= xxx ; concentration
P_RUV=F*THETA(x1)
A_RUV=THETA(x2)
SD=SQRT(P_RUV*P_RUV + A_RUV*A_RUV)
CUMD=PHI((LOQ-F)/SD)
IF (FLG.EQ.0) THEN ; FLG=0, MDV=0, non-LLOQ values
F_FLAG=0
Y=F + SD*ERR(1)
ENDIF
IF (FLG.EQ.1) THEN ; FLG=1, MDV=0, LLOQ values
F_FLAG=1
Y=CUMD
ENDIF

$SIGMA 1 FIXED

$EST METHOD=1 LAPLACIAN