Example_ arclestat in lenstool

[Soniya Sharma]

Hello LENSTOOLers ,

I am in the process of learning of how lenstool works and was trying out the examples already present in the lenstool 6.8 folder.

However while trying the arclestat example, I dont understand how it reads the arclets because the nfw_arclet.cat has many points. So do all these arclets belong to the same source with redshift 1.24 ? And also how the optimization works. I have attached a screenshot of the terminal when the lenstool is running. I am not very sure what does the last line in the screenshot mean??

Looking forward for help :) Thanks

Soniya

[Johan Richard]

Dear Soniya,

This particular example uses as input many individual shear measurements with a fiducial redshift source at z=1.24 indeed. They are not
from the same source as they are used for weak-lensing mass reconstruction, not strong lensing. The last line you get when you run the optimisation shows
the burn-in phase of the optimisation (1st part), with a number going from 0 to 1. At 1 it enters the sampling phase and will start
writing individual models.

The main value you are interested in is “18329.113” in your case which is the chi2 (total chi2), and you can watch it gets lower and lower
as optimisation progresses. The value -3.931 is the evidence. The rest of the numbers are here to show status and/or speed calculation :
next to the burn-in number is a running integer of each step, the last number is computation speed.

I hope this helps,

Johan

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[Soniya Sharma]

Hi Johan,

Thanks for an early reply. 

So basically the situation is like: there are many galaxies at Redshift 1.24 weakly sheared by the potential defined in the example. And lenstool uses those arclets to optimize the model. 

I hope I got it correct!

Thanks again

Soniya

[Michael Hansen]

Dear Soniya

For me it also seems like something is very wrong with your NFWg limits. Alpha should be around 0.01-1.70. Maybe you should run lenstool_tab again.

Cheers,
Michael

[Soniya Sharma]

Thanks Michael for pointing that out. I tried running lenstool again. And this time the limits it shows are (0,0) for alpha. However I notice that in the gnfw profile the limits for alpha are set to be (0.5,1.5). So thats confusing me.

[Eric Jullo]

Dear Soniya

In order to rebuild your lens tool_tab file, you need to go to the root directory and type

make table

Did you do that?
Eric