向量 dot cross product 点积叉积 几何意义 有向量 a b 点积 a * b = |a| * |b| * cosθ 几何意义: 1. a * b == 0,则 a ⊥ b 2. a * b > 0,a b 同向 3. a * b < 0,a b 异向 4. 我们可以 normalize a 和 b,则 |a|,|b| 都为1,那么 cosθ = a*b,在知道 cosθ 的情况下,我们可以求知 a 在 b 上的投射长度 |a| * cosθ,b 在 a 上的投射长度 |b|…

https://www.khanacademy.org/math/linear-algebra/vectors-and-spaces/dot-cross-products/v/vector-dot-product-and-vector-length 忘光光了…

参考的是<游戏和图形学的3D数学入门教程>,非常不错的书,推荐阅读,老外很喜欢把一个东西解释的很详细. 1.向量点积(Dot Product) 向量点积的结果有什么意义?事实上,向量的点积结果跟两个向量之间的角度有关. 2.向量叉积(Cross Product) 两个向量a,b,它们的叉积表示为axb,这个很容易跟数学中两个数字之间的相乘,但是这里是完全不同的. 两个向量叉积在图形坐标中就很直观了,axb同时垂直与a和b. 我们很容易验证axb是否同时垂直a和b向量.根据向量乘积的知识,我们只…

参考:Wiki Cross product…

Cross Product These are two vectors: They can be multiplied using the "Cross Product" (also see Dot Product) The Cross Product a × b of two vectors is another vector that is at right angles to both: And it all happens in 3 dimensions! Calculatin…

Problem D Morley’s Theorem Input: Standard Input Output: Standard Output Morley’s theorem states that that the lines trisecting the angles of an arbitrary plane triangle meet at the vertices of an equilateral triangle. For example in the figure below…

Pipe Time Limit: 1000MS   Memory Limit: 10000K Total Submissions: 9723   Accepted: 2964 Description The GX Light Pipeline Company started to prepare bent pipes for the new transgalactic light pipeline. During the design phase of the new pipe shape th…

在 [Berselli, Luigi C.; Córdoba, Diego. On the regularity of the solutions to the 3D Navier-Stokes equations: a remark on the role of the helicity. C. R. Math. Acad. Sci. Paris 347 (2009), no. 11-12, 613--618] 中, 作者证明了如果$$|u(x+y,t)\cdot \om(x,t)|\leq…

在 [Chae, Dongho; Lee, Jihoon. On the geometric regularity conditions for the 3D Navier-Stokes equations. Nonlinear Anal. 151 (2017), 265--273] 中, 作者证明了如果$$u\times \f{\om}{|\om|}\cdot \f{\vLm^\be u}{|\vLm^\be u|}\in L^p(0,T;L^q(\bbR^3)),\quad \f{2}{p}…

在 [Lee, Jihoon. Notes on the geometric regularity criterion of 3D Navier-Stokes system. J. Math. Phys. 53 (2012), no. 7, 073103, 6 pp] 中, 作者证明了如果$$\f{u}{|u|}\times \f{\om}{|\om|}\cdot \f{\n\times \om}{|\n\times \om|}$$充分小, 则解光滑.…