Hints for Detecting NaNs and Infinities

Prism provides expressions that you can use to detect NaNs (values that are "not a number") and infinities in your data. These expressions derive from the way NaNs and infinities are defined in the IEEE standard for floating-point arithmetic.

To find out if x is a NaN, use the expression:

(x .ne. x)

For example, if x is an array, issue the command

(prism) where (x .ne. x) print x

to print only the elements of x that are NaNs. (The print command is discussed in Chapter 5, Visualizing Data.)

Also, note that if there are NaNs in an array, the mean of the values in the array will be a NaN. (The mean is available via the Statistics selection in the Options menu of a visualizer--see Chapter 5, Visualizing Data.)

To find out if x is an infinity, use the expression:

(x * 0.0 .ne. 0.0)