The above Java 1.1.1 applet is for drawing fundamental domains for congruence subgroups acting on the upper-half plane. Sometimes updating the screen does not work properly, and I don't yet know why. This page is not yet finished, and the program is still under development. I have only really tested this program with one browser on one computer, so I would be intersted to know how it works on other computers.
Any comments are very much appreciated.
Scale is in pixels per unit. If you click on 'expand rectangle' the scale changes so the height of the rectangle becomes the height of the screen. In this mode the triangles can be moved to give a different fundamental domain for the same group, by clicking on the yellow circles on the boundary. Click again to change colour back. Currently only matrices of determinant 1 are allowed, for convenience at points in computation, but I will probably change this later.