# Macro Elements on the double Clough-Tocher Split

The Clough-Tocher Macro Panel lets you impose symmetric super smoothness conditions on the Clough-Tocher split and then check if a macro element can be built with those conditions.

To obtain the macro panel select the configuration "Clough-Tocher", and clock on the button "macro elements" in the control panel. The buttons on the macro panel have the following effects:

• Hide cause the macro panel to disappear. To make it reappear click again on "macro elements".

• Draw causes the current smoothness conditions to be drawn initially, or if the linear algebra in the drawing window has been initialized. (Otherwise the smoothness conditions are drawn automatically whenever they are changed.)

• Init initializes the linear algebra (and exits super selection mode) in the drawing window.

• Set initializes the linear algebra if necessary and attempts to set the natural data that go with the current set of smoothness conditions and the current polynomial degree.

• Clear removes all super smoothness conditions.

• The status window gives information about the current analysis in some situations.

Super smoothness conditions can be imposed using the text fields in the second row of the macro panel, and the buttons to either side of those text fields. The text fields lists the additional degree of smoothness. So if all the text fields show zero then the spline is the ordinary space without super smoothness conditions at all.

The types of smoothness conditions that can be imposed are listed below. To understand the labels on the macro panel recall the labeling of the vertices: , , , and are the boundary vertices,

is the centroid, and is the subcentroid opposite , . For example,

The phrase "" below refers to super smoothness at all four subcentroids, and refers to super smoothness along edges for the centroid the subcentroid since is the centroid, and is a subcentroid.

The following groups of super smoothness conditions are available:

• boundary vertex
• Centroid
• Subcentroids
• boundary edges
• edges from a boundary vertex to the centroid
• edges from a boundary vertex to a subcentroid
• edges from the centroid to a subcentroid
• a face containing a boundary edge and the centroid
• a face containing a boundary edge and a subcentroid
• a face containing a boundary vertex, the centroid, and a subcentroid

## Natural Data

The natural data are the same as for the single Clough-Tocher split.

## C2 Macro Schemes

The following links let you explore the possibility of constructing a C2 macro scheme of degree 9.