Re: [NMusers] Problem with initial values of the omega matrix with nonmem 7.6

[Philip Harder Delff]

Hi Sebastian,

It looks like Nonmem 7.6 is right? Notice, there is a slight difference 
in the 7.6 and the 7.4.4 example. There is a negative eigenvalue in the 
first example but not in the second.


library(NMdata)
om1 <- NMreadInits(lines="$OMEGA BLOCK(3)
+ 0.1000E+01
+                   0.4000E+01   0.1000E+01
+                   0.4000E+01   0.5000E+01   0.8000E+01
+ ") |>
+     dt2mat(col.value="init")
eigen(om1)$values
[1] 13.05750679  0.02484605 -3.08235284

om2 <- NMreadInits(lines="$OMEGA BLOCK(3)
+                 0.1070E+00
+                   0.4800E-01   0.1100E+00
+                   0.4200E-01   0.5600E-01   0.8400E-01
+ ") |>
+     dt2mat(col.value="init")
eigen(om2)$values
[1] 0.19875329 0.06301735 0.03922935

Best,
Philip


On 2026-03-18 05:57 AM, Sebastiaan Sassen wrote:
Dear colleagues,

 I ran into a problem with the omega matrix in nonmem 7.6 for a model
I received (simple FOCE+I advan3 trans4 nothing special).

 In the model file it is specified like this (I tried different
notations as simple decimals, scientific notation etc. to no avail):

 $OMEGA BLOCK(3)
   0.107                ; CL
    0.48E-1 0.11           ; V1
    0.42E-1 0.56E-1 0.084  ; V2

 However, with nonmem 7.6 I get a problem with the initial estimates
of omega. If I look at the list file I see that it is due to my omega
block, which makes sense as the correlations between these values used
as initial values of etas are not valid (outside of -1,1). However,
these initial estimates are not the ones I provided. Compare this to
the same exact model ran on nonmem 7.4.4. Here the initial omega
estimates are as described in the model and it runs well.

 Even in a clean folder without any files other than the dataset (csv)
and the model file (mod).
 Am I doing something wrong or is this something else?

 Nonmem 7.6:

 INITIAL ESTIMATE OF OMEGA HAS A NONZERO BLOCK WHICH IS NUMERICALLY
NOT POSITIVE DEFINITE

 0INITIAL ESTIMATE OF OMEGA:
  BLOCK SET NO.   BLOCK
                    FIXED
         1
                      NO
                   0.1000E+01
                   0.4000E+01   0.1000E+01
                   0.4000E+01   0.5000E+01   0.8000E+01

 Compared to nonmem 7.4.4, which seems to do this correctly:
     
 0INITIAL ESTIMATE OF OMEGA:
  BLOCK SET NO.   BLOCK
                    FIXED
         1
                      NO
                   0.1070E+00
                   0.4800E-01   0.1100E+00
                   0.4200E-01   0.5600E-01   0.8400E-01

 Best regards,

 Sebastiaan