声明时强制功能评估 [英] Force function evaluation on declaration

问题描述

我有一个函数 f[x_,y_,z_]:=Limit[g[x+eps,y,z],eps->0]; 并且我绘制了 f[x,y,z] 下一步.之前，我曾经在 f 的定义中计算限制并复制表达式.我试图一步完成这一切.但是，只有当我尝试绘制 f 时，才会对限制进行评估.结果，每次我改变变量并重新绘制时，都会重新评估限制(评估大约需要一分钟，所以很烦人).我尝试先评估限制，然后执行 f[x_,y_,z_]:=%.但这也行不通.如何获得在声明时评估限制的函数?

I have a function f[x_,y_,z_]:=Limit[g[x+eps,y,z],eps->0]; and I plot f[x,y,z] in the next step. Earlier, I used to evaluate the limit and copy the expression in the definition of f. I tried to make it all in one step. However, the evaluation of the Limit is done only when I try to plot f. As a result, every time I change around the variables and replot, the limit is evaluated all over again (it takes about a min to evaluate, so it becomes annoying). I tried evaluating the limit first, and then doing f[x_,y_,z_]:=%. But that doesn't work either. How do I get the function to evaluate the limit upon declaration?

推荐答案

Mr Wizard 的一个替代方案是，您还可以将 Evaluate 放在函数的定义中:

An alternative to Mr Wizard's solution is that you can also put the Evaluate in the function's definition:

f[x_, y_, z_] := Evaluate[Limit[Multinomial[x, y, z], x->0]]

Plot3D[f[x, y, z], {y, 1, 5}, {z, 1, 5}]

您可以通过 Timing Plot 将两个版本与没有 Evaluate 的版本进行比较.

You can compare the two versions with the one without an Evaluate by Timing the Plot.

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