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# 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 the dim_sum_Wrap function if metadata retention is desired. The interface is identical.

## 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)

; Use dim_sum_Wrap if metadata retention is desired
; qav = dim_sum_Wrap(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)

; Use dim_sum_Wrap if metadata retention is desired
; 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.

```    xSumTime = dim_sum( x(lat|:, lon|:, time|:) )    ; ==> xSumTime(nlat,nlon)

; Use dim_sum_Wrap if metadata retention is desired
; xSumTime = dim_sum_Wrap( x(lat|:, lon|:, time|:) )    ; ==> xSumTime(lat,lon)

xSumTime = dim_sum_n( x, 0 )                     ; no reordering needed

; Use dim_sum_n_Wrap if metadata retention is desired
xSumTime = dim_sum_n_Wrap( x, 0 ) ; no reordering needed
```