log

Table of Contents

Description

The log function object computes the natural logarithm of an input volScalarField.

\[ f = s \ln(max(f_0, a)) + t \]

where

\( f \) = Output volScalarField
\( f_0 \) = Input volScalarField
\( \ln \) = Natural logarithm operator
\( a \) = Clip scalar
\( s \) = Scaling factor
\( t \) = Offset factor

Operands

Operand Type Location
input volScalarField $FOAM_CASE/<time>/<inpField>
output file - -
output field volScalarField $FOAM_CASE/<time>/<outField>

Usage

Example of the log function object by using functions sub-dictionary in system/controlDict file: 

log1
{
    // Mandatory entries (unmodifiable)
    type            log;
    libs            (fieldFunctionObjects);

    // Mandatory (inherited) entry (runtime modifiable)
    field           <inpField>;

    // Optional entries (runtime modifiable)
    clip            1e-3;
    checkDimensions false;
    scale           1.0;
    offset          0.0;

    // Optional (inherited) entries
    result          <fieldResult>;
    region          region0;
    enabled         true;
    log             true;
    timeStart       0;
    timeEnd         1000;
    executeControl  timeStep;
    executeInterval 1;
    writeControl    timeStep;
    writeInterval   1;
}

where the entries mean:

Property Description Type Required Default
type Type name: log word yes -
libs Library name: fieldFunctionObjects word yes -
field Name of the operand field word yes -
clip Value to clip the operand field values to prevent zero or negative input scalar no SMALL
checkDimensions Flag to check dimensions of the operand field bool no true
scale Scaling factor - s above scalar no 1.0
offset Offset factor - t above scalar no 0.0

The inherited entries are elaborated in:

Example by using the postProcess utility: 

postProcess -func "log(<inpField>)" -scale 1.0 -offset 0.0

Further information

Tutorial:

Source code:

History

  • Introduced in version v2006