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MathGroup Archive 2005

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Re: How does NIntegrate suppress messages?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg62614] Re: How does NIntegrate suppress messages?
  • From: Andrew Moylan <andrew.moylan at anu.edu.au>
  • Date: Tue, 29 Nov 2005 04:46:21 -0500 (EST)
  • References: <dm95bd$6q1$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Excellent, thanks Ingolf. I think your post answers all the questions 
about this topic.

Ingolf Dahl wrote:
> Hi
> A general method to suppress messages from Check is the following:
> 
>   Block[{$Messages = {}}, Check[expr, failexpr]]
> 
> My theory is that Nintergrate uses the same mechanism. Can we find a way to
> unsuppress the messages? 
> 
> One example:
> 
>   func[x_]:=1/x;
> 
>   x=0;Check[func[x],"Divide by zero"]
> 
> gives both a message and evalutated failexpr, but 
> 
>   x = 0; Block[{Set[$Messages, {}]}, Check[func[x], "Divide by zero"]]
> 
> just evaluates failexpr. We might turn on the messages by redefining the
> function:
> 
>   newfunc[x_] := Block[{Set[$Messages, {OutputStream["stdout", 1]}]},
> func[x]];
> 
>   x = 0; Block[{Set[$Messages, {}]}, Check[newfunc[x], "Divide by zero"]]
> 
> will give us the message back. To apply the same on NIntegrate is a bit
> tricky.Define first 
>  
>   f::err = "error"; f[x_?NumericQ] := ( Message[f::err]; x ) 
> 
> Then 
> 
>   NIntegrate[f[x], {x, 0, 1}]
> 
> will give no messages. Embedd f in a new function in the following ways:
> 
>    newf[ x_?NumericQ]:= ( Block[ { $MessageList=msl, $Messages= {
> OutputStream[     "stdout",1]}}, { f[x], msl=$MessageList}[[1]]])
>  
>   msl = {}; NIntegrate[newf[x], {x, 0, 1}]
> 
> will then give you error messages. The NumericQ test is essential.
> 
> Best regards
> 
> Ingolf Dahl
> Sweden
> 
> 
> 
> 
>>-----Original Message-----
>>From: Andrew Moylan [mailto:andrew.moylan at anu.edu.au] 
To: mathgroup at smc.vnet.net
>>Sent: den 25 november 2005 08:25
>>Subject: [mg62614]  Re: How does NIntegrate suppress messages?
>>
>>It's quite a mystery. My guess is that NIntegrate temporarily 
>>redefines the Message[...] function.
>>
>>Personally, I want to know because I want to copy this 
>>behaviour of NIntegrate for my own functions, if it is easy. 
>>Often I write code that uses Check, and I don't want the 
>>messages generated and appearing as errors and clogging up the output.
>>
>>"Alan" <info at optioncity.REMOVETHIS.net> wrote in message 
>>news:dm499k$srh$1 at smc.vnet.net...
>>
>>>"Andrew Moylan" <andrew.moylan at anu.edu.au> wrote in message 
>>>news:dm1b0v$ic1$1 at smc.vnet.net...
>>>
>>>>Whenever the integrand in NIntegrate generates messages 
>>
>>(by calling 
>>
>>>>Message), the output of these messages are suppressed, 
>>
>>although they 
>>
>>>>are still generated in the sense that they can be caught 
>>
>>using Check. 
>>
>>>>Does anyone know how NIntegrate does this?
>>>
>>>I don't, but your post answers a question of mine about 
>>
>>behavior which 
>>
>>>has always seemed a puzzle. Often I will wrap a complicated 
>>>computation in a Check in order to Abort[] on any message. Then, I 
>>>will sometimes get an Abort[], but no message! And, indeed, 
>>
>>often an 
>>
>>>NIntegrate is involved. When that occurs, I have never been able to 
>>>re-write the code to retrieve those missing messages.
>>>So if there is a way to "unsuppress", that will be helpful 
>>
>>to me, too.
>>
>>>regards,
>>>alan
>>>
>>>
>>
>>
>>
> 
> 


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