54 lines
1.5 KiB
Plaintext
54 lines
1.5 KiB
Plaintext
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{{alias}}( W )
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Returns an accumulator function which incrementally computes a moving
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product.
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The `W` parameter defines the number of values over which to compute the
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moving product.
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If provided a value, the accumulator function returns an updated moving
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product. If not provided a value, the accumulator function returns the
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current moving product.
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As `W` values are needed to fill the window buffer, the first `W-1` returned
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values are calculated from smaller sample sizes. Until the window is full,
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each returned value is calculated from all provided values.
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For accumulations over large windows or accumulations of large numbers, care
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should be taken to prevent overflow. Note, however, that overflow/underflow
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may be transient, as the accumulator does not use a double-precision
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floating-point number to store an accumulated product. Instead, the
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accumulator splits an accumulated product into a normalized fraction and
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exponent and updates each component separately. Doing so guards against a
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loss in precision.
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Parameters
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----------
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W: integer
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Window size.
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Returns
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-------
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acc: Function
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Accumulator function.
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Examples
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--------
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> var accumulator = {{alias}}( 3 );
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> var p = accumulator()
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null
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> p = accumulator( 2.0 )
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2.0
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> p = accumulator( -5.0 )
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-10.0
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> p = accumulator( 3.0 )
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-30.0
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> p = accumulator( 5.0 )
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-75.0
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> p = accumulator()
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-75.0
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See Also
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--------
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