getRandomDiffRmsInMas¶

lsst.validate.drp.util.getRandomDiffRmsInMas(array)[source]¶

Calculate the RMS difference in mmag between a random pairs of magnitudes.

Returns:

float

RMS difference

See also

getRandomDiff: Get the difference

Notes

The LSST SRD recommends computing repeatability from a histogram of magnitude differences for the same star measured on two visits (using a median over the magDiffs to reject outliers). Because we have N>=2 measurements for each star, we select a random pair of visits for each star. We divide each difference by sqrt(2) to obtain RMS about the (unknown) mean magnitude, instead of obtaining just the RMS difference.

Examples

>>> mag = [24.2, 25.5]
>>> rms = getRandomDiffRmsInMas(mag)
>>> print(rms)
212.132034