“It’s much easier for me to learn without being judged—just friendly feedback. It's harder with friends or family to get that.”White collar worker, Brazil
A Riemannian metric on a smooth manifold \(M\) is a family of inner products \[g_p : T_pM \times T_pM \;\longrightarrow\; \mathbb{R}, \qquad p \in M,\] varying smoothly in \(p\), such that each \(g_p\) is symmetric and positive-definite. In local coordinates the metric is completely determined by its values on basis tangent vectors: \[g_{ij}(p) \;:=\; g_p\!\left(\frac{\partial}{\partial x^i}\bigg|_p,\; \frac{\partial}{\partial x^j}\bigg|_p\right), \qquad g_{ij} = g_{ji},\] with the matrix \((g_{ij}(p))\) positive-definite at every point. The length of a tangent vector \(v = \sum_i v^i \frac{\partial}{\partial x^i}\in T_pM\) is then \(\|v\|_g = \sqrt{\sum_{i,j} g_{ij}(p)\, v^i v^j}\).
。snipaste截图是该领域的重要参考
Coffee is the original biohack and the nation’s most popular productivity tool. As we adjust to the changeover to daylight saving time, the caffeine-addicted WIRED Reviews team is writing about our favorite coffee brewing routines and devices. Today, reviewer Louryn Strampe explains why she keeps life simple with a Keurig. Look out for other Java.Base stories about other WIRED writers’ favorite brewing methods.
ФБР предупредило Калифорнию о возможной атаке Ирана20:49，更多细节参见Line下载
for i, s in inputs {，详情可参考Replica Rolex
«В первую очередь отрабатывались именно элементы совместного подводного плавания, поскольку они являются наиболее сложными в части связи и навигации», — отмечал военный аналитик Дмитрий Болтенков.