# negdist

Negative distance weight function

## Syntax

```Z = negdist(W,P) dim = negdist('size',S,R,FP) dw = negdist('dz_dw',W,P,Z,FP) ```

## Description

`negdist` is a weight function. Weight functions apply weights to an input to get weighted inputs.

`Z = negdist(W,P)` takes these inputs,

 `W` `S`-by-`R` weight matrix `P` `R`-by-`Q` matrix of `Q` input (column) vectors `FP` Row cell array of function parameters (optional, ignored)

and returns the `S`-by-`Q` matrix of negative vector distances.

`dim = negdist('size',S,R,FP)` takes the layer dimension `S`, input dimension `R`, and function parameters, and returns the weight size [`S`-by-`R`].

`dw = negdist('dz_dw',W,P,Z,FP)` returns the derivative of `Z` with respect to `W`.

## Examples

Here you define a random weight matrix `W` and input vector `P` and calculate the corresponding weighted input `Z`.

```W = rand(4,3); P = rand(3,1); Z = negdist(W,P) ```

## Network Use

You can create a standard network that uses `negdist` by calling `competlayer` or `selforgmap`.

To change a network so an input weight uses `negdist`, set `net.inputWeights{i,j}.weightFcn` to `'negdist'`. For a layer weight, set `net.layerWeights{i,j}.weightFcn` to `'negdist'`.

In either case, call `sim` to simulate the network with `negdist`.

## Algorithms

`negdist` returns the negative Euclidean distance:

```z = -sqrt(sum(w-p)^2) ```