Bugs item #1121342, was opened at 2005-02-12 06:37
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Status: Open
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Priority: 5
Submitted By: Nobody/Anonymous (nobody)
Assigned to: Nobody/Anonymous (nobody)
Summary: Implementation of Monotone Spline
Initial Comment:
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The implementation of the Hyman filter for the
monotonising of the cubic spline is wrong. The Hyman
constraints are corrrectly specified but are applied to the
second derivative of the function (y'') rather than to y'.
In order to implement correctly you need to
i) solve for the y'' values at the node in the usual way
ii) compute the first derivative values y' at each node
iii) generate the appropriate lagrange cubic polynomials
through the node points with the correct y' value at the
ends.
The incorrect approach does not guarantee to produce
monotone splines.
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