# Thermodynamic output options

The `Thermo` class computes and prints thermodynamic information to the
screen and log file; see the files `thermo.cpp` and `thermo.h`.

There are four styles defined in `thermo.cpp`: \"one\", \"multi\",
\"yaml\", and \"custom\". The \"custom\" style allows the user to
explicitly list keywords for individual quantities to print when
thermodynamic output is generated. The others have a fixed list of
keywords. See the [thermo_style](thermo_style) command for a list of
available quantities. The formatting of the \"custom\" style defaults to
the \"one\" style, but can be adapted using [thermo_modify
line](thermo_modify).

The thermo styles (one, multi, etc) are defined by lists of keywords
with associated formats for integer and floating point numbers and
identified but an enumerator constant. Adding a new style thus mostly
requires defining a new list of keywords and the associated formats and
then inserting the required output processing where the enumerators are
identified. Search for the word \"CUSTOMIZATION\" with references to
\"thermo style\" in the `thermo.cpp` file to see the locations where
code will need to be added. The member function `Thermo::header()`
prints output at the very beginning of a thermodynamic output block and
can be used to print column headers or other front matter. The member
function `Thermo::footer()` prints output at the end of a thermodynamic
output block. The formatting of the output is done by assembling a
\"line\" (which may span multiple lines if the style inserts newline
characters (\"n\" as in the \"multi\" style).

New thermodynamic keywords can also be added to `thermo.cpp` to compute
new quantities for output. Search for the word \"CUSTOMIZATION\" with
references to \"keyword\" in `thermo.cpp` to see the several locations
where code will need to be added. Effectively, you need to define a
member function that computes the property, add an if statement in
`Thermo::parse_fields()` where the corresponding header string for the
keyword and the function pointer is registered by calling the
`Thermo::addfield()` method, and add an if statement in
`Thermo::evaluate_keyword()` which is called from the `Variable` class
when a thermo keyword is encountered.

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::: title
Note
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The third argument to `Thermo::addfield()` is a flag indicating whether
the function for the keyword computes a floating point (FLOAT), regular
integer (INT), or big integer (BIGINT) value. This information is used
for formatting the thermodynamic output. Inside the function the result
must then be stored either in the `dvalue`, `ivalue` or `bivalue` member
variable, respectively.
::::

Since the [thermo_style custom](thermo_style) command allows to use
output of quantities calculated by [fixes](fix), [computes](compute),
and [variables](variable), it may often be simpler to compute what you
wish via one of those constructs, rather than by adding a new keyword to
the thermo_style command.