Sigma Clipping Page (1-D Fit Package)
The Sigma Clipping page sets the parameters that control iterative data rejection in the 1-D Fit procedure. This process iterates, or cycles, to reject points and re-calculate the fit until some completion test is passed. At each cycle, the fit is performed and, for each point, its distance above or below the fit is compared with the standard deviation of the fit. If a point is too deviant, it is marked for rejection. When all points have been tested, the fit is re-computed using only the remaining points. criterion. Iteration stops when either the specified maximum number of iterations is reached or no more points are rejected. Example
Rejection is based on the "n-sigma" algorithm, in which the standard deviation, sigma, is multiplied by some number, n, to determine the rejection threshold. The value of sigma is updated each iteration. The current method modified the n-sigma method by allowing different values for the upper and lower clipping thresholds, n.
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Sigmas Above |
The value, n, in the n-sigmas upper threshold. Values further than n-sigmas above the fit will be rejected from it. |
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Sigmas Below |
The value, n, in the n-sigmas lower threshold. Values further than n-sigmas below the fit will be rejected from it. |
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Iterations |
The maximum number of iterations, or cycles, of data rejection. Mira will take an "early out" to exit the iteration before this value if no more points are rejected. |