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Further Examples: SetDelayed (:=)

Here 2 x is evaluated and assigned to be the value of ff[x]. Neither ff[3] nor ff[y] have values.

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Here x is given the value 4. This evaluates 2 x at x = 4 and assigns the resulting value to ff[x].

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Again, neither ff[3] nor ff[y] have values.

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This evaluates 2 x at x = 4 and assigns the resulting value to ff[x_].

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Since represents any expression, ff[x_] always evaluates to .

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Here ff is defined using SetDelayed.

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With SetDelayed, 2 x is not evaluated until ff is called with one argument.

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See also the Further Examples for Set.