Re: Expanding function names to explicit formulas

• To: mathgroup at smc.vnet.net
• Subject: [mg8164] Re: [mg8104] Expanding function names to explicit formulas
• From: David Withoff <withoff>
• Date: Sat, 16 Aug 1997 11:51:07 -0400
• Sender: owner-wri-mathgroup at wolfram.com

```> Hello,
>
> Is there any way to convert input or output that includes function
> names (say, Erf[x]) to its explicit mathematical form (with the integral
> symbol and such)?
>
> Regards.
> --
>   __|__
> ___\_/___   Paulo Mouat,
>    ___      mouat at mail.telepac.pt
>   |___|     http://www.geocities.com/Vienna/8804/
>   |___|

You can do this in the same way that you can convert an output such
as the integer 4 into its explicit mathematical form 2+2:

In[5]:= 4 /. 4 -> HoldForm[2+2]

Out[5]= 2 + 2

If you release the hold, then Mathematica will convert 2+2 into 4, and
will likewise convert the integral represention of Erf[x] into Erf[x].

In[14]:= convert[p_] := p /. Erf[x_] ->
HoldForm[2/Sqrt[Pi] Integrate[Exp[-t^2], {t, 0, x}]]

In[15]:= result = convert[Erf[x]]

2
2 Integrate[Exp[-t ], {t, 0, x}]
Out[15]= --------------------------------
Sqrt[Pi]

In[16]:= ReleaseHold[result]

Out[16]= Erf[x]

Dave Withoff
Wolfram Research

```

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