[Gmsh] partition operation and inconsistency on the partition numbers

[Umut Tabak]

Dear developers,

I have run into a problem reading the partitioning information formed by 
Gmsh, by Chaco.

Looking at the manual gives

$Elements
number-of-elements
elm-number elm-type number-of-tags < tag > ... node-number-list
...
$EndElements

and the partition number in tag section does not seem to be on the 3rd 
tag as mentioned in the manual as below but the 4th entry

number-of-tags
           gives the number of integer tags that follow for the n-th 
element. By default,
           the first tag is the number of the physical entity to which 
the element belongs;
           the second is the number of the elementary geometrical entity 
to which the
           element belongs;
           **** the third is the number of mesh partitions to which the 
element belongs****, // this line,
           followed by the partition ids (negative partition ids 
indicate ghost
           cells). A zero tag is equivalent to no tag.

Some clarification is appreciated at this point.

Best regards,

Umut

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