# parabolaSlopes

##### Estimate the slope of an interpolating function using a parabola

Returns estimates of the slope of an interpolating function that runs through a set of points in the xy-plane.

##### Usage

`parabolaSlopes(x,y)`

##### Arguments

- x,y
coordinates of points defining the interpolating function.

##### Value

Returns an estimate of the slope of the interpolant at (x,y).

##### Note

This function is used as part of the Stineman
interpolation function `stinterp`

.
It is rarely called directly by the user,
and checking of x and y must be performed by the calling function.

The parabola method provides a better approximation of the slope for smooth functions
than the original method suggested by Stineman (1980), which is provided by
the function `stinemanSlopes`

(see the documentation
of the function `stinterp`

for further information),
but it results in higher slopes near abrupt steps or spikes
and can lead to some overshooting where Stineman's method does not.

##### See Also

`stinterp`

and `stinemanSlopes`

.

##### Examples

```
# NOT RUN {
x <- seq(0,2*pi,by=pi/6)
y <- sin(x)
# }
# NOT RUN {
parabolaSlopes(x,y)
# }
```

*Documentation reproduced from package stinepack, version 1.3, License: GPL-2*