R: Re: good list

• To: mathgroup at smc.vnet.net
• Subject: [mg125152] R: Re: good list
• From: "Brambilla Roberto Luigi (RSE)" <Roberto.Brambilla at rse-web.it>
• Date: Sat, 25 Feb 2012 01:52:55 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <201202231045.FAA07331@smc.vnet.net>

```Dear Alexej,
It works fine!
Many thanks again, Roberto.

===============
Myfunc involves a Cauchy Principal Value integral on a finite interval that often fails when applied to an interpolated function.

somelist={..,{xi,fi},..};
fo=Interpolation[somelist];
myfunc[x_]:=CauchyPrincipalValue[fo[u]/(u-x),{u,a,{x},b}] (*verMath5.1*)

nstep=100;
mylist=Table[{x,myfunc[x],{x,a,b,(b-a)/nstep}];

-----Messaggio originale-----
Da: Alexei Boulbitch [mailto:Alexei.Boulbitch at iee.lu]
Inviato: gioved=EC 23 febbraio 2012 11.45
A: mathgroup at smc.vnet.net
Oggetto: Re: good list

Hi to all,

I have a function  myfunc[x] (of some complexity) and I want to build
the list of its values in the interval (a<=x<=b) with step
dx=(b-a)/nstep

nstep=100;

mylist=Table[{x,myfunc[x],{x,a,b,(b-a)/nstep}];

According to the input value, sometimes myfunc[x] is not able to give a
numeric result

(in my case a singular difficult numerical integral) . In others cases
it works fine.

My question is how to build the list with only the good cases.

Many thanks, Roberto

Hi, Roberto,

Try this:

myFunc[x_]:=NIntegrate[Exp[-x*y^2],{y,0,\[Infinity]}]//Quiet;

Select[Table[{x,If[NumericQ[myFunc[x]]//Quiet,myFunc[x]]},{x,-1,1,0.1}],#[[2]]=!=Null&]
{{5.55112*10^-17,1.18945*10^8},{0.1,2.8025},{0.2,1.98166},{0.3,1.61802},{0.4,1.40125},{0.5,1.25331},{0.6,1.14411},{0.7,1.05924},{0.8,0.990832},{0.9,0.934165},{1.,0.886227}}

Have fun, Alexei
Alexei BOULBITCH, Dr., habil.
IEE S.A.
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```

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