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Schrödinger required that a [[wave packet]] solution near position <math>\mathbf{r}</math> with wave vector near <math>\mathbf{k}</math> will move along the trajectory determined by classical mechanics for times short enough for the spread in <math>\mathbf{k}</math> (and hence in velocity) not to substantially increase the spread in {{math|'''r'''}}. Since, for a given spread in {{math|'''k'''}}, the spread in velocity is proportional to Planck's constant <math>\hbar</math>, it is sometimes said that in the limit as <math>\hbar</math> approaches zero, the equations of classical mechanics are restored from quantum mechanics.<ref name="Analytical Mechanics 2008">''Analytical Mechanics'', L. N. Hand, J. D. Finch, Cambridge University Press, 2008, {{isbn|978-0-521-57572-0}}</ref> Great care is required in how that limit is taken, and in what cases.

Schrödinger required that a [[wave packet]] solution near position <math>\mathbf{r}</math> with wave vector near <math>\mathbf{k}</math> will move along the trajectory determined by classical mechanics for times short enough for the spread in <math>\mathbf{k}</math> (and hence in velocity) not to substantially increase the spread in {{math|'''r'''}}. Since, for a given spread in {{math|'''k'''}}, the spread in velocity is proportional to Planck's constant <math>\hbar</math>, it is sometimes said that in the limit as <math>\hbar</math> approaches zero, the equations of classical mechanics are restored from quantum mechanics.<ref name="Analytical Mechanics 2008">''Analytical Mechanics'', L. N. Hand, J. D. Finch, Cambridge University Press, 2008, {{isbn|978-0-521-57572-0}}</ref> Great care is required in how that limit is taken, and in what cases.

薛定谔要求一个靠近位置<math>\mathbf{r}</math>的[[wave packet]]解，其波矢量在<math>\mathbf{k}</math>附近，将沿着经典力学确定的轨迹移动足够短的时间，以使<math>\mathbf{k}</math>中的传播（因此在速度上）不会实质性地增加<math>\mathbf{k}</math>中的传播{{数学|''r''}}。因为，对于{math |''k''}中的给定扩散，速度扩散与普朗克常数成正比，所以有时有人说，当<math>\hbar</math>接近零时，经典力学的方程就从量子力学中恢复了。<ref name=“analytic mechanics 2008”>“analytic mechanics”，五十、 N.Hand，J.D.Finch，剑桥大学出版社，2008，{isbn | 978-0-521-57572-0}</ref>在如何确定极限以及在何种情况下，需要非常小心。

薛定谔要求一个靠近位置<math>\mathbf{r}</math>的[[wave packet]]解，其波矢量在<math>\mathbf{k}</math>附近，将沿着经典力学确定的轨迹移动足够短的时间，以使<math>\mathbf{k}</math>中的传播（因此在速度上）不会实质性地增加<math>\mathbf{k}</math>中的传播{{数学|''r''}}。因为，对于{math |''k''}中的给定扩散，速度扩散与普朗克常数成正比，所以有时有人说，当<math>\hbar</math>接近零时，经典力学的方程就从量子力学中恢复了。<ref name="Analytical Mechanics 2008">''Analytical Mechanics'', L. N. Hand, J. D. Finch, Cambridge University Press, 2008, {{isbn|978-0-521-57572-0}}</ref> 在如何确定极限以及在何种情况下，需要非常小心。

\eta^2=0  \\

\eta^2=0  \\