Professor Ha-Joon Chang is inspired by his passion for food to reflect on why economics matters - or, as he puts it, “a hungry economist explains the world”.
For the Poincaré half-space model in dimension 2, the metric evaluates on the coordinate tangent vectors \(\frac{\partial}{\partial x}, \frac{\partial}{\partial y} \in T_pM\) as \[g_p\!\left(\frac{\partial}{\partial x^i}\bigg|_p,\;\frac{\partial}{\partial x^j}\bigg|_p\right) = \frac{1}{y^2}\,\delta_{ij},\] i.e. the coordinate tangent vectors are orthogonal and each has length \(\frac{1}{y}\) — shrinking to zero as \(p\) approaches the boundary \(y\to 0\), which is what makes the space “infinitely large” near the boundary.
（二）货物的保险价值，是保险责任开始时货物在起运地的发票价格或者非贸易商品在起运地的实际价值以及运费和保险费的总和；，更多细节参见新收录的资料
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