Here we review the syntax of mathematical expressions. Any user who wishes to use VISTA effectively should review this section carefully.
Arithmetic expressions come in four types:
The following table lists arithmetic functions supported in VISTA, with examples of their use. ('Binary' means relating two objects - 'unary' means applying to one object.)
The following logical operators are also supported.
|logical greater than||AB||A2.5|
|logical less than||AB||A100|
|==||logical equal to||A==B||A==10|
|=||logical not equal to||A =B||A =10|
|=||logical less than or equal to||A=B||A=5|
|=||logical greater than or equal to||A=B||A=3|
Logical operators return a value of either 1 (true) or 0 (false).
Expressions are evaluated in the same order as they are in FORTRAN. You
may change the order of evaluation using parentheses "()". An example is
VISTA supports a variety of functions. The argument to the function is contained in square brackets. The following functions are currently supported:
Examing/Editing Image Data:
Functions may be used as arguments of other functions. Functions can contain expressions of arbitrary complexity (so long as the parentheses are balanced and there are no extraneous spaces!).
Variable names or arithmetic expressions may be used ANYWHERE an explicit
constant may be used in keyword-value expressions. Recall that such an
expression has an 'option=value' construction. For example, if you wanted
to plot row 200 of image 4 over columns X to X+50, (where X is some
variable) you could say
Note that R, XS, and XE are keywords, not variables and the equal sign following them is not interpreted as an arithmetic operation. However, since everything following the first = is an arithmetic expression, you could save the 'value' of, for instance, XE, by doing the following
The variable XLAST takes on the value of X+50.