Appendix III

AFGEN function

AFGEN stands for Arbitrary Function GENerator (Subroutine AFGen). It is a function which is used for linear interpolation in a one-dimensional array with paired data. Uneven places in the array represent the X-values, whereas the Y-values are represented by the even places. Such an array can describe the dependency of variable Y on variable X when no mathematical description is available or is too cumbersome. A plotted example is depicted in Figure AIII_1:

Figure AIII_1 Linear interpolation

The array belonging to this example has to be filled as:

Arguments of the AFGEN function in order of their place in the argument list are: name of the table, number of pairs, X value to be interpolated. The X-values have to be arranged from low to high values and are not allowed to be interchanged. Every X-value has to precede its connected Y-value.

Three situations for interpolation can occur:

1) The argument x at which interpolation should take place is less or equal to the first X-value in the array. The Y-value is set to the first Y-value in the array.

2) The argument x value at which interpolation should take place is between the first and the last X-value in the array. The Y-value can now be found via linear interpolation. First the X values left and right from the argument x have to be detected, then the Y-value can be calculated: 3) The argument x at which interpolation should take place is equal to or larger then the last X-value in the array. The Y-value is set to the last Y-value in the array.