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MathGroup Archive 2006

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Re: question about Block

  • To: mathgroup at smc.vnet.net
  • Subject: [mg69685] Re: [mg69661] question about Block
  • From: "Chris Chiasson" <chris at chiasson.name>
  • Date: Thu, 21 Sep 2006 07:28:57 -0400 (EDT)
  • References: <200609200644.CAA24396@smc.vnet.net>

I that the numerical functions like FindMinimum, NIntegrate, etc, do
weird things with the message system, usually to suppress the messages
(and no, I'm not talking about General::stop).

If you don't mind, post a summary when you find something.

On 9/20/06, dimmechan at yahoo.com <dimmechan at yahoo.com> wrote:
> Hello to all.
>
> Block as it is well known to the members of this forum does have some
> nice applications.
> For example
>
> $Version
> "5.2 for Microsoft Windows (June 20, 2005)"
>
> Block[{Message}, Integrate[1/x, {x, -1, 2}]]
> Infinity
> Block[{Message}, NIntegrate[Sin[x]/x, {x, 0, Infinity}]]
> 2.6457805920701
>
> (execute the commands without Block to see the messages)
>
> Let me now define a list of two functions.
>
> lst = {1/x, 1/x^2};
>
> Then
>
> NIntegrate[lst, {x, 1, 2}]
> \!\(NIntegrate::"inum" : "Integrand \!\({1\/x,
>      1\/x\^2}\) is not numerical at \!\({x}\) = {1.5`}."\)
> NIntegrate[lst, {x, 1, 2}]
>
> because NIntegrate has the attribute HoldAll
>
> Attributes[NIntegrate]
> {HoldAll, Protected}
>
> Of course
>
> NIntegrate[Evaluate[lst], {x, 1, 2}]
> {0.693147180559947, 0.5000000000000211}
>
> Now to my surprise I discovered that the following commands fail to
> prevent the appearance of  NIntegrate::inum  message.
>
> Block[{Message}, NIntegrate[lst, {x, 1, 2}]]
> \!\(NIntegrate::"inum" : "Integrand \!\({1\/x,
>      1\/x\^2}\) is not numerical at \!\({x}\) = {1.5`}."\)
> NIntegrate[lst, {x, 1, 2}]
>
> Block[{$Messages = {}}, NIntegrate[lst, {x, 1, 2}]]
> \!\(NIntegrate::"inum" : "Integrand \!\({1\/x,
>      1\/x\^2}\) is not numerical at \!\({x}\) = {1.5`}."\)
> NIntegrate[lst, {x, 1, 2}]
>
> What is more strange is that the relevant Plot::plnr message can be
> prevented.
>
> Plot[lst, {x, 1, 2}, DisplayFunction -> Identity];
> Plot::plnr : lst is not a machine-size real number at x =
> 1.0000000416666666`. (...3 times...)
> General::stop : Further output of Plot::plnr will be suppressed during
> this \
> calculation.
>
> Attributes[Plot]
> {HoldAll, Protected}
>
> Block[{Message}, Plot[lst, {x, 1, 2}, DisplayFunction -> Identity]];
> Block[{$Messages = {}}, Plot[lst, {x, 1, 2}, DisplayFunction ->
> Identity]];
>
> Of course someone can simply switch off the message.
>
> Off[NIntegrate::inum]
> NIntegrate[lst, {x, 1, 2}]
> NIntegrate[lst, {x, 1, 2}]
>
> On[NIntegrate::inum]
>
> but the question remains why exist this strange (at least for me)
> situation.
>
> Any comments/suggestions?
>
> Dimitris
>
>


-- 
http://chris.chiasson.name/


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