A Geometry Fan

A geometry is kind of fun. Here is some memos about that.

• Dihedral angle is not a normal difference on a manifold mesh. 2007-07-12
  When I computed edge mean curvature defined in Polthier[2] or Cohen-Steiner[3], a plane has some curvature. This is how I made a stupid mistake.
• Reflection Line in 3 minutes 2009-05-07
  What is the reflection line. I try to explain it in 3 minutes.
• Why parallelogram area is |x1 y2 - x2 y1|? 2011-07-10
  my blog

Mathematics is also fun, but it's difficult. (Difficult things are usually fun.)

• Big balls and Small balls 2008-02-03
  One day I chatted with my friend. She told me her children took a test of mathematics and we told about it. I showed the answer of that. But one thing was missing, which was how to explain it to children. This article is such a trial. ``Can I explain simultaneous equations to 10 year old child?''
• 大きなボールと小さなボール (Japanese translation of big balls and small balls) 2008-05-18
  これは上記の文書の日本語訳です．ある日，私の友人の子供が私学の試験を 受けたという話になりました．その場で答えを出したは良いのですが，さて これは10歳の子供には難しすぎ，どうやって説明したら良いのかということ が頭に残りました．この文書はそうやってできました．「10歳の子供に連立 一次方程式を説明できるだろうか」というのはこの文書を書く動機になり ました．