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runave_n

Calculates an unweighted running average on the given dimension.

Prototype

	function runave_n (
		x        : numeric,  
		nave [1] : integer,  
		opt  [1] : integer,  
		dim  [1] : integer   
	)

	return_val [dimsizes(x)] :  float or double

Arguments

An array with one or more dimensions. The dim-th dimension will be the dimension on which the unweighted running average is performed. Missing values should be indicated by x@_FillValue. If x@_FillValue is not set, then the NCL default (appropriate to the type of x) will be assumed.

nave

Number of points to be included in the running average.

opt

End-point option (opt = 0 is the most common option)

In the following:

N = {last point in the series, i.e. N = npts - 1}
xi = {input series}
xo = {output series}

opt < 0 : utilize cyclic conditions             
           e.g., nave = 2 
                 xo(0) = (xi(0) + xi(1))/nave
                 xo(N) = (xi(N) + xi(0))/nave
           e.g., nave = 3
                 xo(0) = (xi(N) + xi(0) + xi(1)) / nave
                 xo(N) = (xi(N - 1) + xi(N) + xi(0)) / nave
           e.g., nave = 4
                 xo(0) = (xi(N) + xi(0) + xi(1) + xi(2)) / nave
                 xo(N) = (xi(N - 1) + xi(N) + xi(0) + xi(1)) / nave

opt = 0 : set unsmoothed beginning and end pts to x@_FillValue [most common]
           e.g., nave = 2 
                 xo(0) = (xi(0) + xi(1)) / nave
                 xo(N) = xi@_FillValue
           e.g., nave = 3
                 xo(0) = xi@_FillValue  
                 xo(1) = (xi(0) + xi(1) + xi(2)) / nave
                 xi(N) = xi@_FillValue    
           e.g., nave = 4 
                 xo(0) = xi@_FillValue 
                 xo(1) = (xi(0) + xi(1) + xi(2) + xi(3)) / nave
                 xo(N - 2) = (xi(N - 3) + xi(N - 2) + xi(N - 1) + xi(N)) / nave
                 xo(N - 1)= xi@_FillValue
                 xo(N)= xi@_FillValue

opt > 0 : utilize reflective (symmetric) conditions
           e.g., nave = 2 
                 xo(0) = (xi(0) + xi(1)) / nave
                 xo(N) = (xi(N) + xi(N-1)) / nave
           e.g., nave = 3 
                 xo(0) = (xi(1) + xi(0) + xi(1)) / nave
                 xo(N) = (xi(N - 1) + xi(N) + xi(N-1)) / nave
           e.g., nave = 4 
                 xo(0) = (xi(2) + xi(1) + xi(0) + xi(1)) / nave
                 xo(N) = (xi(N - 1) + xi(N) + xi(N - 1) + xi(N - 2)) / nave

dim

A scalar integer indicating which dimension of x to do the calculation on. Dimension numbering starts at 0.

Return value

Returns an array dimensioned the same x.

The return type is floating point if the input is floating point, and double if the input is of type double.

Description

This function returns an array of the same dimensionality as x with the dim-th dimension smoothed.

The running average is a special case of a filter where all weights are the same. The filter is applied to the i-th time of the requested series as follows:

F(i) = SUM{UF(i - (nave / 2) + j)} / nave for j = 0, nave - 1

where F is the filtered field, UF is the unfiltered field, and nave is the number of elements in the running average.

If the number of weights is even, the filter's center falls between series elements; in this case, the center is shifted one-half of a time increment towards the latter element.

Use the runave_n_Wrap function if metadata retention is desired. The interface is identical.

Examples

Example 1

Let x be dimensioned nlat x mlon x ktimes where nlat = 64, mlon = 128, and ktimes = 1000. Perform a 3 point running average and use opt = 0. Return the smoothed value to the original x array:

  x = runave_n (x, 3, 0, 2)

  ; Use runave_n_Wrap if metadata retention is desired
  ; x = runave_n_Wrap (x, 3, 0, 2)

Example 2

Let x be dimensioned ntimes x nlat x mlon with named dimensions "time" , "lat" , "lon". To perform smoothing on the "time" dimension:

    nave = 31
    opt  = 0
    y    = runave_n (x, nave, opt, 0)

    ; Use runave_n_Wrap if metadata retention is desired
    ; y    = runave_n_Wrap (x, nave, opt, 0)

y will be a 3-dimensional array of length time x nlat x mlon.

Example 3

Let x be dimensioned ntimes x klev x nlat x mlon with named dimensions. Perform a 5 point running average use the cyclic option in the longitude direction: