**Syntax**

` >>>> PRIOR: prior_info`

**Parent Command**

all third-level commands in block` > PARAMETER`

**Subcommand**

` -`

**Description**

This command provides the prior information of the parameter to be estimated. If command `>>>> PRIOR` is omitted, the value from the TOUGH2 input file is taken. Prior information is only effective if a standard deviation is provided (see command `>>>> DEVIATION` (p)), in which case the difference between the parameter estimate and its prior value is penalized in the objective function. The starting point for the optimization is given through commands `>> GUESS` and `>>>> GUESS.` If command `>>>> LOGARITHM` is present, the prior information is the logarithm of the parameter. Similarly, if command `>>>> FACTOR` is present, the prior information should be a multiplication factor (default is 1.0).

**Example**

` > PARAMETER
>> ABSOLUTE permeability
>>> ROCK type : SAND1
>>>> LOGARITHM
>>>> PRIOR information : -12.0
>>>> standard DEVIATION: 1.0 order of magnitude
<<<<
>>> ROCK types: CLAY1 CLAY2 CLAY3 BOUND
>>>> FACTOR
>>>> initial GUESS : 1.0
>>>> is not WEIGHTed : 0.0 (default)
<<<<
<<<`

>> GUESS, i.e., starting point for optimization

1 -13.0

<<

**See Also**

` >> GUESS | >>>> GUESS | >>>> DEVIATION (p) | >>>> VARIATION
`