Transport and Sorption - Environmental Modeling - page 121

The sorption -switch has to be set to an integer between 0 and 3. For tracers it
should be set to 0, for linear sorption to 1, for Freundlich sorption to 2 and for
Langmuir sorption to 3. Depending on the sorption-switch, the variables k1 and k2
contain different variables. In case of Freundlich and Langmuir isotherms these two
variables contain the two sorption parameters. In case of linear sorption k1 should
be set to the retardation factor if that is used directly. For the user the alternative is
to give the K d -value in variable k2 . In the latter situation, k1 needs to be set to
0 (not a valid value for retardation) in order to indicate which option is wanted. The
two variables are not used for tracers, i.e. when sorption ¼ 0 .
The two variables rhob and theta contain the bulk density and porosity. These
are used only if the Freundlich or Langmuir retardation factors are calculated or if R
is to be calculated from the K d -value for the linear isotherm. Some re-calculations
have to be performed before the pdepe -function is called 5 :

For the linear isotherm the retardation factor is calculated in the second line of
these commands. In the fourth line, bulk density and porosity are multiplied
with the first factor of the Freundlich- or Langmuir-sorption parameters. This
is done in order to reduce the number of variables to be transferred to the function
sub-routines. The call is lengthy even with that cosmetic:

The parameter list in the second line needs to appear in all functions of the
M-file. The only place where the new introduced variables are needed is the
transfun -function. The following statements need to be included in the function
before the assignment of the other variables:

5 & is the logical 'and' operator; for other logical operators see MATLAB

help under 'logical

®

array functions'; the logical 'or' operator is: | .