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A value known to be numeric at compile time is represented as a
double. PSPP provides three values of double for
special purposes, defined in data/val-type.h:
The system-missing value, used to represent a datum whose true value is unknown, such as a survey question that was not answered by the respondent, or undefined, such as the result of division by zero. PSPP propagates the system-missing value through calculations and compensates for missing values in statistical analyses. See Missing Observations in PSPP Users Guide, for a PSPP user’s view of missing values.
PSPP currently defines SYSMIS as -DBL_MAX, that is, the
greatest finite negative value of double. It is best not to
depend on this definition, because PSPP may transition to using an
IEEE NaN (not a number) instead at some point in the future.
The greatest finite negative (except for SYSMIS) and positive
values of double, respectively. These values do not ordinarily
appear in user data files. Instead, they are used to implement
endpoints of open-ended ranges that are occasionally permitted in PSPP
syntax, e.g. 5 THRU HI as a range of missing values
(see MISSING VALUES in PSPP Users Guide).