Description Usage Arguments Value Note Author(s) References See Also Examples

Returns estimates of the slope of an interpolating function that runs through a set of points in the xy-plane. The slopes are calculated using to the algorithm of Stineman (1980), i.e. from the tangent of circles passing through every three consecutive points.

1 | ```
stinemanSlopes(x,y,scale=FALSE)
``` |

`x,y` |
coordinates of points defining the interpolating function. |

`scale` |
if true (default) then the x and y values are normalized prior to the slope calculation. |

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

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.

Stineman's method provides a more robust interpolating function
near abrupt steps or spikes in the point sequence
than the alternative method based on a second degree interpolating polynomial,
which is provided by the function `parabolaSlopes`

(see the documentation
of the function `stinterp`

for further information),
but it results in slightly less accuracy for smooth functions.

Tomas Johannesson

Stineman, R. W. *A Consistently Well Behaved Method of Interpolation.*
Creative Computing (1980), volume 6, number 7, p. 54-57.

`stinterp`

and `parabolaSlopes`

.

1 2 3 4 5 |

```
[1] 1.116638e+00 7.932212e-01 3.535473e-01 0.000000e+00 -3.535473e-01
[6] -7.932212e-01 -9.549297e-01 -7.932212e-01 -3.535473e-01 5.434010e-17
[11] 3.535473e-01 7.932212e-01 1.116638e+00
[1] 1.098788e+00 8.110713e-01 4.407481e-01 2.268417e-17 -4.407481e-01
[6] -8.110713e-01 -9.549297e-01 -8.110713e-01 -4.407481e-01 -1.587892e-16
[11] 4.407481e-01 8.110713e-01 1.098788e+00
```

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