Energy principle and variational method note 11: shape function (a dimension reduction idea)

Shape function ( A dimension reduction idea , An infinite number of degrees of freedom ( impact ) The function of is regarded as a shape function )

$In\; approximate\; solution,\; shape\; function\; is\; called\; potential\; function$

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$$\begin{gathered} notes\; ：\; among{u}_1(x)=\frac{x^2}{L_1^2}It\; is\; assumed\; that\; the\; form\; of\; the\; shape\; function\; is\; not\; quadratic \\ Others\; are\; the\; same\; as\; the\; first \end{gathered}$$