Expressions

ADF supports the use of arithmetic expressions, functions, and constants to represent numerical data. This can be convenient for the input of, for instance, atomic positions when these would most easily be represented in terms of 1/3, sin(360/5), et cetera. Using expressions and functions is easier, avoids the tedious typing of long decimal expansions and solves the question of precision (how many digits should be supplied?).

The standard arithmetic operands in Fortran (+ - * / **) can be applied in expressions, together with parentheses where suitable.

Blanks are allowed and ignored, but they are interpreted as separators, i.e. as denoting the end of an expression, whenever the part until the blank can be evaluated as a correct expression. For instance 3* 4 will be interpreted as 12, but 3 *4 will be interpreted as 3, followed by a character *, followed in turn by the number 4.

All numbers and results are interpreted and handled as being of type real, but whenever the result is a whole number (allowing for very small round-off) it will be recognized and accepted as an integer when such data is required.