Re: FindRoot in 5.0
- To: mathgroup at smc.vnet.net
- Subject: [mg42856] Re: [mg42819] FindRoot in 5.0
- From: Eric Mockensturm <emm10 at psu.edu>
- Date: Wed, 30 Jul 2003 19:31:12 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Oh...
And using
Developer`SetSystemOptions["EvaluateNumericalFunctionArgument" ->False]
did not change the time it took in 5.0 to any significance.
On Wednesday, July 30, 2003, at 09:38 AM, Richard Gass wrote:
>
> On Wednesday, July 30, 2003, at 04:07 AM, Eric Mockensturm wrote:
>
>> I realize that FindRoot has changed but there seems to be a
>> fundamental difference in it between pre-5.0 versions and 5.0 that
>> breaks most of my notebooks. Maybe I've been following bad
>> 'programming' practices all these years, but....
>>
>> Anyway, a simple illustration follows.
>>
>> In 4.2:
>>
>> In[7]:=func[x_]:=(y=x;NIntegrate[BesselY[1/2,s],{s,1/2,y}])
>> In[8]:=FindRoot[(Print[x];func[x]),{x,2,4}]
>> Out[8]={x\[Rule]3.04729}
>>
>> In 5.0:
>>
>> In[1]:=func[x_]:=(y=x;NIntegrate[BesselY[1/2,s],{s,1/2,y}])
>> In[2]:=FindRoot[(Print[x];func[x]),{x,2,4}]
>> Out[2]={x\[Rule]4.}
>>
>> with errors...
>>
>> NIntegrate::nlim: s = x is not a valid limit of integration
>>
>> It seems that 5.0 is trying to evaluate func[x] symbolically before
>> start to search for a root. How do I make a global change to this
>> behavior. Does it have something to do with the HoldAll attribute?
>> FindRoot was been HoldAll in 4.2, too.
>>
>>
>>
>>
>
> This effects more than just FindRoot but you can restore the old
> behavior by using
> Developer`SetSystemOptions["EvaluateNumericalFunctionArgument" ->
> False] . This restores the old behavior but you take a substantial
> speed hit. In your case you can fix the problem (without the speed
> hit) by using
>
>> func[x_?NumericQ]:=(y=x;NIntegrate[BesselY[1/2,s],{s,1/2,y}])
>
> and then
>> FindRoot[func[x],{x,2,4},EvaluationMonitor:>Print[x]]
> or better yet
> points={}
> FindRoot[func[x],{x,2,4},EvaluationMonitor:>AppendTo[points,x]]
> ListPlot[points]
>
>
> Richard Gass
> Department of Physics
> University of Cincinnati
>