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Re: := vs = in some function definitions

• To: mathgroup at smc.vnet.net
• Subject: [mg113257] Re: := vs = in some function definitions
• From: Pierre Albarede <pa.news at free.fr>
• Date: Thu, 21 Oct 2010 07:00:47 -0400 (EDT)
• References: <i9m7u7$j41$1@smc.vnet.net>

On Oct 20, 10:06 am, Sam Takoy <sam.ta... at yahoo.com> wrote:

> Have read everything I could find regarding delayed assignment, I'm
> still not quite sure when to use which.
>
> For example, in the definition
>
> f[x_] = IdentityMatrix[50].Append[Range[1, 49], x];
>
> could there ever be any reason to use :=   ?


If x has a value when you evaluate your definition, il will be used in
the definition, which is not usually what you want.
For example, try :

x = 4

Clear@f; f@x_ = 2 x

?f