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## spline problem

**From**: |
Paul Wellner Bou |

**Subject**: |
spline problem |

**Date**: |
Mon, 10 Jul 2006 15:31:34 +0200 |

**User-agent**: |
Thunderbird 1.5 (X11/20051201) |

Hi,

`Yesterday I tried to calculate a spline with three points given and with
`` hermit boundary conditions. Octave was not able to give me a spline
``with a continous first derivative in the point where the tow polynoms meet.
`
For example:
The points:
(0,0), (1,0), (3,0)
The boundary conditions:
S'(0) = 10
S'(3) = 0
Calculating the spline with
csape([0 1 3], [0 0 0], 'complete', [10 0]);

`gives me a spline with matches exactly the given conditions but the
``first derivative in (1,0) is not continuous. Octave gives me that spline:
`
P =
6.00000 -16.00000 10.00000 0.00000
-0.50000 2.00000 -2.00000 0.00000

`Thats very nice, but p0'(1) = -4 and p1'(0) = -2 (considering that the
``origin of p1 is (1,0)). Is there any way to add this condition? To say
``octave that it should calculate a spline with a continuous first derivative?
`
There is a solution, so that's not the problem.
P =
6.66667 -16.66667 10.00000 0.00000
-0.83333 3.33333 -3.33333 0.00000

`And, by the way, why does octave warns me with "Warning: empty y range
``[0:0], adjusting to [-1:1]" plotting three points with an y-vector [0 0
``0]? And what does it mean by "adjusting to [-1:1]? What is adjusted here?
`
Regards
Paul.

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**spline problem**,
*Paul Wellner Bou* **<=**