| .. 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``. That will typically be much | |
| faster than using `numpy.ma.MaskedArray`. | |