[tag] expression

Second-derivative expressions w.r.t. an unordered pair of variables. Each entry stores the VariablePair - where (v1, v2) and (v2, v1) are treated as identical - together with multi-component expressions corresponding one-to-one with the value expressions. Specified in the project file as:

<d2value>
  <variable_name>temperature</variable_name>
  <variable_name>phase_pressure</variable_name>
  <expression>d2f1/dT dp</expression>
  <expression>d2f2/dT dp</expression>
</d2value>

Additional info

No additional info.

Used in the following test data files

Used in no end-to-end test cases.