Hi,

I want to know how to use non_negative_difference() corresponding implementation in kapacitor.

I am able to use non_negative_derivative() using following

```
|derivative('value')
.unit(1s)
.nonNegative()
.as('value')
```

I am also able to use difference()

```
|difference('var_value')
.as('value')
```

But I am not able to find the implementation of non_negative_difference()

I tried to use following, but alerts are not firing correctly

```
|derivative('var_value')
.nonNegative()
.as('value')
|difference('value')
.as('value')
```

Can anyone suggest right way to use non_negative_difference()

Regards,

Advait Deo