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MathGroup Archive 2012

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Re: Why does the order of down values come back?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg124788] Re: Why does the order of down values come back?
  • From: Shizu <slivo.vitz at msa.hinet.net>
  • Date: Tue, 7 Feb 2012 04:00:36 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com

In[]:= g[x_ + y_] := op1[x, y]; g[x_ y_] := op2[x, y]

In[]:= DownValues[g]
Out[]:= {HoldPattern[g[x_ + y_]] :> op1[x, y], HoldPattern[g[x_ y_]] :> op2[x, y]}

In[]:= DownValues[g] = Reverse[DownValues[g]]
Out[]:= {HoldPattern[g[x_ y_]] :> op2[x, y], HoldPattern[g[x_ + y_]] :> op1[x, y]}

In[]:= DownValues[g]
Out[]:= {HoldPattern[g[x_ y_]] :> op2[x, y], HoldPattern[g[x_ + y_]] :> op1[x, y]}

===================================================
What I did here does NOT make sense either.
But after reordering, the original order doesn't come back.
This one is predictable.

Actually, we can even define the previous function as follows:
In[]:= f[n_] := f[n - 1] + f[n - 2];
       f[1] := 1;
       f[0] := 0;

In[]:= f[10]
Out[]:= 55

The order we set up the function is not important.
Any comments?
Thanks.



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