Coefficient functions

Coefficient functions are defined as list of constants/functions. Each element corresponds to a sub-domain, or a boundary condition number.

define coefficient coef_lam  10,15, -5, (5*x), (sin(y)),

Functions must be put into brackets. Function may be built as described in Section 3.1, but may now additionally contain variables.

Predefined variables are $x$, $y$, and $z$ for the Cartesian coordinates.

Specifying too many coefficients is ok, too less will lead to an error.

Note: Now, the coordinates are $x1$, $x2$, and $x3$, will change to $x$, $y$, and $z$.