Prev: Find (cyclic) Sequence
Next: Download as Live Mathematica from Wolfram|Alpha
From: David Bailey on 24 Apr 2010 03:59
mokambo wrote:

>
> Following your suggestions I tried:
>
> PowerMod[___] := "N/A";
>
> but it does not work unless you unprotect the symbol (a bad idea)
>
> Attributes[PowerMod]
> = {Listable, Protected, ReadProtected}
>
> So I searched through the docs and found:
>
> Check[PowerMod[3, -1, 288], "N/A"]
>

If you really want this effect, why not use Unprotect - you can always
use Protect after you have made the change! (Note that these changes
only affect the in-core copy of the function - no permanent change is made!)

Check is all very well, but some functions - such as Integrate - can
return unevaluated without giving a message. I would supply your own
function that calls the real function internally, for example:

In[498]:= MyIntegrate[x__] := Module[{ans},
ans = Integrate[x];
If[Head[ans] === Integrate,
"N/A",
ans
]
];

In[499]:= MyIntegrate[f[x], x]

Out[499]= "N/A"

In[500]:= MyIntegrate[Sin[x], x]

Out[500]= -Cos[x]

David Bailey
http://www.dbaileyconsultancy.co.uk

First  |  Prev  | 
Pages: 1 2
Prev: Find (cyclic) Sequence
Next: Download as Live Mathematica from Wolfram|Alpha