[Gmsh] write a .pos file and read it back -> different results

[Christophe Geuzaine]

Al Danial wrote:

> I'm trying to write a program that writes .pos files and am having a
> hard time getting the sequence of terms just right.  Probably one of
> those ubiquitous "off by one" goofs somewhere.  I figured a good way
> to get the format right is to match the  output that gmsh itself
> writes.
> 
> I start with this file (called "A.pos"):
> 
> View "vname_A" {
> ST(0.5,0.5,0.0,1.0,0.5,0.0,1.0,1.0,0.0){1,2,3,4,5,6,7,8,9,10};
> ST(0.5,0.5,0.0,1.0,1.0,0.0,0.5,1.0,0.0){2,3,4,5,6,7,8,9,10,11};
> };
> 
> I load it into gmsh and it looks fine.  Then I do "Save as/ASCII
> view..." and write the view to the file "B.pos".  It looks like this:
> 
> $PostFormat /* Gmsh 1.2, ascii */
> 1.2 0 8
> $EndPostFormat
> $View /* vname_A */
> vname_A 3 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
>  0 1 2 0.5 1 1 0.5 0.5 1 0 0 0 1 2 3 4 5 6 7 8 9 10 0.5 1 0.5 0.5 1 1
> 0 0 0 2 3 4 5 6 7 8 9 10 11
> $EndView
> 
> The problem is that when B.pos is loaded back in it does not resemble
> A.pos at all.
> 
> What am I missing?          -- Al

Your first file is wrong: for a scalar triangle the number of values has
to be a multiple of 3 (1 number for each node, times the number of steps).

You could for example have:

View "vname_A" {
ST(0.5,0.5,0.0,1.0,0.5,0.0,1.0,1.0,0.0){1,2,3,4,5,6,7,8,9};
ST(0.5,0.5,0.0,1.0,1.0,0.0,0.5,1.0,0.0){2,3,4,5,6,7,8,9,10};
};


PS: Gmsh should definitely output a warning or an error when this
occurs... I'll add a sanity check in the code.

-- 
Christophe Geuzaine
Applied and Computational Mathematics, Caltech
geuzaine at acm.caltech.edu - http://geuz.org