# Parameter Format

Each command may have zero or more parameters. Most command parameters have default values.

The parameter values are persistent, in the sense that they change only if the command is issued with that parameter. For example, the density parameter in DENSITY_MODEL has a default value of one. If you issue the following commands:
DENSITY_MODEL( "air" ) {
density = 1.225
}
DENSITY_MODEL( "air" ) {
expansivity = 0.0039
}

the value of the density parameter of the density model "air" is 1.225, the value of expansivity is 0.0039 and the remaining parameters have their respective default values.

Each parameter has one of the following seven types:
• String
• Enumerated
• Boolean
• Integer
• Real
• List
• Array