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Centroid（形心）
+ Z8 C3 d( f* K8 KIn geometry, the centroid or barycenter of an object X in n-dimensional space is the intersection of all hyperplanes that divide X into two parts of equal moment about the hyperplane. Informally, it is the "average" of all points of X.
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# }- Q4 Z! X3 M4 E/ cThe geometric centroid of a physical object coincides with its center of mass if the object has uniform density, or if the object's shape and density have a symmetry which fully determines the centroid. These conditions are sufficient but not necessary.+ _4 Z1 D5 u# C0 ]% [1 J
8 j, t1 s. I {The centroid of a finite set of points can be computed as the arithmetic mean of each coordinate of the points.
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In geography, the centroid of a region of the Earth's surface is often known as its geographic center.+ y7 y3 ]4 V7 d c7 a1 D( d
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Neutral axis（中性轴）
: B$ n) `3 ^. AAn axis in the cross section of a beam, shaft or the like along which there are no longitudinal stresses / strains. If the section is symmetric (in both geometry and materials) the neutral axis is at the geometric centroid.- m+ v& O, e. n; w+ g U
这个也许能有些帮助。 | 
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