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The 
Sketcher BSplineDecreaseKnotMultiplicity tool decreases the multiplicity of a B-spline knot.
- Select a B-spline knot.
- There are several ways to invoke the tool:
- Press the [
Decrease knot multiplicity button. - Select the Sketch → Sketcher B-spline tools → Decrease knot multiplicity option from the menu.
- Press the [
See Sketcher_BSplineIncreaseKnotMultiplicity
If you decrease the multiplicity of a knot to zero, the knot vanishes. Mathematically it then appears zero times in the knot vector, meaning there is no longer a basis function. Understanding this requires some math, but it will also be clear if you look at the multiplicity. For example a knot with multiplicity 0 on a B-spline with degree 3 means that at the position of the knot two Bézier pieces are connected with C^3^ continuity. So the third derivative should be equal on both sides of the knot. However for a cubic Bézier curve this means that both sides must be part of the same curve. There is then effectively no longer a knot connecting two Bézier curves.
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