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Re: double loop

  • To: mathgroup at smc.vnet.net
  • Subject: [mg113051] Re: double loop
  • From: "Sjoerd C. de Vries" <sjoerd.c.devries at gmail.com>
  • Date: Tue, 12 Oct 2010 04:26:10 -0400 (EDT)
  • References: <i8s5f9$93p$1@smc.vnet.net> <i8uklb$ocu$1@smc.vnet.net>

Exact numbers may have an impact on speed and memory use, though. I
remember one PseudoInverse calculation I did many years ago on a 20x90
matrix where I forgot to use reals (this was when I just started using
Mathematica). This took my physics Dept. mainframe a week to calculate
and resulted in a matrix of 20 MB, because all matrix entries
consisted of ratios of very long integers. At that time, my mac had an
internal memory of 4 MB. Problems were of a different order then...

Cheers -- Sjoerd

On Oct 11, 11:16 am, "Nasser M. Abbasi" <n... at 12000.org> wrote:
> On 10/10/2010 3:44 AM, maria giovanna dainotti wrote:
>
> > Dear All,
> > I cleared up the notebook but when I plot the picture I don't recover t=
he
> > contour plot desidered.=C2  The colours should be the different corre=
lation
> > coefficient and it is not the case.
> > I will be grateful if you could help
> > Maria
> > =C2
> > h=0.71
> > ckms=299792.5
> > HubE[z_,Om_,Ol_]:=SQRT(Om*(1+z)^3+Ol)dL[z_,Om_,Ol_,h_]:=3.0856*1018=
*106*ckms/(100*h)*(1+z)*NIntegrate[1/HubE[z,Om,Ol],{z,0,z},MaxRecursion
>
> > ->100]
> > TabOmegalambda=Table[i,{i,0.1,1.1,0.05}]
> > TabOmegaM=Table[i,{i,0.0,1.0,0.05}]
>
> I can't help you on the code below now. I just want to make a comment on
> the above code.
>
> I think it is better to change the above table commands so they do not
> use floats. Look at the difference
>
> In[168]:= N[TabOmegaM=Table[i,{i,0.0,1.0,0.05}],$MachinePrecision]
>
> Out[168]= {0.,
> 0.05,
> 0.1,
> 0.15000000000000002,
> 0.2,
> 0.25,
> 0.30000000000000004,
> 0.35000000000000003,
> 0.4,
> 0.45,
> 0.5,
> 0.55,
> 0.6000000000000001,
> 0.65,
> 0.7000000000000001,
> 0.75,
> 0.8,
> 0.8500000000000001,
> 0.9,
> 0.9500000000000001,
> 1.}
>
> vs.
>
> In[167]:= N[TabOmegaM=Table[i,{i,0,1,1/20}],$MachinePrecision]
> Out[167]= {
> 0,
> 0.05000000000000000,
> 0.1000000000000000,
> 0.1500000000000000,
> 0.2000000000000000,
> 0.2500000000000000,
> 0.3000000000000000,
> 0.3500000000000000,
> 0.4000000000000000,
> 0.4500000000000000,
> 0.5000000000000000,
> 0.5500000000000000,
> 0.6000000000000000,
> 0.6500000000000000,
> 0.7000000000000000,
> 0.7500000000000000,
> 0.8000000000000000,
> 0.8500000000000000,
> 0.9000000000000000,
> 0.950000000000000,
> 1.000000000000000}
>
> You see the difference?
>
> Those Units of Least Precision (ULP) differences can sometimes end up
> accumulating and might cause more differences in later computation.
>
> Always *try* to use exact numbers, (this is the advantage of using a CAS
> system, so use it), until to the very end, or until when one must use
> floats (may be for speed or printing, etc...)
>
>
>
> > LxOmegalambda={};
> > Do[
> > Ol=TabOmegalambda[[k]];
> > LxOmegaM={};
> > Do[
> > Om=TabOmegaM[[j]];
> > DataGood={};
> > Do[
> > idGRB=Dataspectrum[[i,1]];
> > z=Dataspectrum[[i,2]];
> > Espectrum=Dataspectrum[[i,3]];
> > Fx=Dataspectrum[[i,4]];
> > beta=Dataspectrum[[i,5]];
> > EisonewOm=4*p*dL[z,Om,Ol,h]2*(1+z)-2*Espectrum;
> > Lx=4*p*dL[z,Om,Ol,h]2*(1+z)-(1+beta)*Fx;
> > AppendTo[DataGood,{EisonewOm,Lx,z,idGRB,Om,O=EF =AC}],{i,1,Length[Datas=
pectrum]}];
> > CLxEiso=N[Correlation[DataGood[[All,1]],DataGood[[All,2]]]];
> > AppendTo[LxOmegaM,{Om,Ol,CLxEiso}],{j,1,Length[TabOmegaM]}];
> > If[Ol+Om<2.2,AppendTo[LxOmegalambda,{LxOmegaM}]],{k,1,Length[TabOmegala=
mbda]}]
> > Flatten[LxOmegalambda,2]
> > ListContourPlot[Flatten[LxOmegalambda,2],PlotRange
> > ->All,FrameLabel
> > ->{"Omega_M ","Omega_lambda"}]
>
> --Nasser



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