Expressions in .prj file

Usability
1

According to this issue, the function to define a certain parameter does not limit to “simple” expressions, but it can be extremely refined, for example using boolean conditions.

I repost here the documentation link:

I personally never tried them (will do asap), but I think it would be useful to have it somewhere in the OGS conventions section (but in the meanwhile I post it here).

2

Hi Lurpi,

indeed, the documentation of the exprtk features in OGS could be better. I’ll try to extend it ASAP. The relevant sections in the Doxygen documentation are rather brief, see:

https://doxygen.opengeosys.org/d9/dfe/ogs_file_param__properties__property__function
https://doxygen.opengeosys.org/d5/dab/ogs_file_param__prj__parameters__parameter__function

for function material properties and parameters, respectively. The pages only say: “For the evaluation of the expressions the exprtk library is used”.

Btw.: Besides “normal” formulas, we have one test in OGS that uses “advanced” features of exprtk:

Tests/Data/ThermoHydroMechanics/Linear/Beam_sealed_bimaterial/square_1e2_function.xml:8:
            <expression>if (x &lt; 2) 19; else if (x &lt; 2.1) 0.95; else 9.5;</expression>

Note: the "<"s have been changed to "&lt;"s to avoid conflicts with the enclosing XML syntax.

However, this test is not easy to find.

Best regards,
Christoph

1 Like
3

I just created an issue for this: Extend function parameter documentation (#3346) · Issues · ogs / ogs · GitLab

1 Like
4

Thanks, yes I tried a similar expression, with the always beautiful nesting of if clauses and it works.

EX_EXPTRK
EX_EXPTRK553×568 12.6 KB

However, I tried the switching case and for the OGS parser it is difficult to understand. I will open an issue

            <expression> switch {                                                       
                        case y > 3 : if (z+20 > y+3) -9e6; else -5e6;;                                               
                        case y < 3 : -7e6;
                        default          : 7.5e6;
                        }    
            </expression>

and the error is

info: Reading project file /projects2/AG3193/aug_22/run/test_functions-expr/test_stress.prj.
Entity: line 418: parser error : StartTag: invalid element name
case y < 3 : -7e6;
^
critical: /projects2/AG3193/ogs_branch/ogsPW/BaseLib/PrjProcessing.cpp:124 replaceIncludes()

please note that

case y > 3

works fine.

Ciao,
Luca

5

maybe everything has to be in one line?

6

no, multiple lines and multiple cases are fine, the issue is with the “<” char. I just saw that the OGS test provides

the "<"s have been changed to "<"s

which is a solution, although it is an obscure one.

7

Sure, this makes sense because < collides with the XML.

8

Cattura

9

No, spaces have meaning in XML. However, <, >, &, ', " are considered as special characters and therefore these need to be replaced the same way as you would do in HTML.

10

I was trying to see if there is a quick fix for the parser. At the moment it reads correctly the >, but not < , from the expressions .

11

I should have read this thread to the end and saved me my longish answer to your GitLab issue :slight_smile:

Like Jörg said above, please use &lt; instead of <. That should work. Actually I already wrote that in my very first answer in this thread :slight_smile: