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.. note that if this is changed from the default approach of using an *include*
(in index.rst) to a separate performance page, the header needs to be changed
from === to ***, the filename extension needs to be changed from .inc.rst to
.rst, and a link needs to be added in the subpackage toctree
.. _astropy-nddata-performance:
Performance Tips
================
+ Using the uncertainty class `~astropy.nddata.VarianceUncertainty` will
be somewhat more efficient than the other two uncertainty classes,
`~astropy.nddata.InverseVariance` and `~astropy.nddata.StdDevUncertainty`.
The latter two are converted to variance for the purposes of error
propagation and then converted from variance back to the original
uncertainty type. The performance difference should be small.
+ When possible, mask values by setting them to ``np.nan`` and use the
``numpy`` functions and methods that automatically exclude ``np.nan``,
like ``np.nanmedian`` and ``np.nanstd``. This will typically be much
faster than using `numpy.ma.MaskedArray`.
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