# numSummationTerms

Change number of summation terms for calculating periodic Green's function

## Syntax

``numSummationTerms(array,num)``

## Description

example

````numSummationTerms(array,num)` changes the number of summation terms used to calculate periodic Green's function of the infinite array. This method calculates $2*num+1$ of the periodic Green's function. The summation is carried out from –`num` to +`num`. A higher number of terms results in better accuracy but increases the overall computation time.```

## Examples

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Create an infinite array with the scan elevation at 45 degrees. Calculate the scan impedance. By default, the number of summation terms used is 21.

```h = infiniteArray(ScanElevation=45); s = impedance(h,1e9)```
```s = 85.0930 +71.2392i ```

Change the number of summation terms to 51. Calculate the scan impedance again.

```numSummationTerms(h,25) s = impedance(h,1e9)```
```s = 85.2389 +71.2731i ```

Change the number of terms to 101. Increasing the number of summation terms results in a more accurate scan impedance. However, the time required to calculate the scan impedance increases.

```numSummationTerms(h,50) s = impedance(h,1e9)```
```s = 85.2841 +71.2777i ```

## Input Arguments

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Infinite array, specified as an `infiniteArray` object.

Example: `infiniteArray(ScanElevation=45)`

Number to calculate summation terms, specified as a scalar. The summation is carried out from –`num` to +`num`.

Example: `50`

## Version History

Introduced in R2015b