Sets new values for the VARIANCE component of an NDF data structure
!
) is given for
the variance, then any pre-existing variance information is erased. "Data"
or "Variance"
. ["Data"]
!
) value is
supplied, the new variance values are determined by the expression given for
Parameter VARIANCE. [!]
"DATA"
implies normal
$\surd N$ error
estimates, whereas VARIANCE="DATA + 50.7"
might be used if a sky background of 50.7
units had previously been subtracted.
If a ‘null’ value (!
) is given for this parameter, then no new VARIANCE component will
be created and any pre-existing variance values will be erased.
All of the standard Fortran 77 intrinsic functions are available for use in the variance expression, plus a few others (see SUN/61 for details and an up-to-date list).
Calculations are performed using real arithmetic (or double precision if appropriate) and are constrained to be non-negative.
The data type of the VARIANCE component is set to match that of the DATA component.