NCL Website header
NCL Home > Documentation > Functions > General applied math

dim_sum

Computes the arithmetic sum of a variable's rightmost dimension at all other dimensions.

Prototype

	function dim_sum (
		x  : numeric   
	)

	return_val  :  float or double

Arguments

x

A variable of numeric type and any dimensionality.

Return value

The output will be double if x is double, and float otherwise.

The output dimensionality is the same as the first n-2 dimensions of the input variable. That is, the dimension rank of the input variable will be reduced by one.

Description

The dim_sum function computes the sum of all elements of the n-1th (rightmost) dimension for each index of the dimensions 0...n-2. Missing values are ignored.

Use dim_sum_n if you want to specify which dimension(s) to calculate the sum on.

Use dim_sum_Wrap if retention of metadata is desired.

See Also

dim_sum_Wrap , dim_sum_n_Wrap , sum, dim_sum_n, dim_median, dim_stddev, dim_num, dim_product, dim_rmsd, dim_rmvmean, dim_rmvmed, dim_standardize, dim_stat4, dim_stddev, dim_variance

Examples

Example 1

Create a variable, q, of size (3,5,10) array. Then calculate the sum of the rightmost dimension.

    q   = random_uniform(-20,100,(/3,5,10/))
    qav = dim_sum(q)   ;==>  qav(3,5)
Example 2

Let x be of size (ntim,nlat,mlon) and with named dimensions "time", "lat" and "lon", respectively. Then, for each time and latitude, the zonal sum (i.e., sum of all non-missing longitudes) is:

    xSumLon = dim_sum( x )    ; ==> xSumLon(ntim,nlat)
Generally, users prefer that the returned variable have metadata associated with it. This can be accomplished via the dim_sum_Wrap function:

    xSumLon = dim_sum_Wrap( x )    ; ==> xSumLon(time,lat)
Example 3

Let x be defined as in Example 2: x(time,lat,lon). Compute the sum over time at each latitude/longitude grid point. Use NCL's Named Subscripting to reorder the input array such that "time" is the rightmost dimension.

Note: in V5.1.1, you will be able to use dim_sum_n to avoid having to reorder your data.

    xSumTime = dim_sum( x(lat|:, lon|:, time|:) )    ; ==> xSumTime(nlat,nlon)
    xSumTime = dim_sum_n( x, 0 )                     ; no reordering needed
If metadata is desired use
    xSumTime = dim_sum_Wrap( x(lat|:, lon|:, time|:) )    ; ==> xSumTime(lat,lon)
    xSumTime = dim_sum_n_Wrap( x, 0 )                     ; no reordering needed