Friday, May 6, 2011

Computing Time

One interesting thing I've realized in trying to compare the 2D auto-correlation with the 3D auto-correlation (on the same files) is that the 2D auto-correlation takes MUCH longer to compute than the 3D. This is strange because in this test they are computing the same number of pairs, well barring some differences in the gridding. I must be doing something very inefficient with the 2D calculation, or measuring pairs out to much larger distances than in the 3D case. The 3D auto-correlation function took less than a minute to compute, and the 2D auto-correlation function is still running, and it's been 51 minutes.

Here are the 2D and 3D autocorrelation functions on the whole set (on big redshift bin)

Below is the 3D and 2D autocorrelation on a smaller (100Mpc/h) redshift bin:

At redshift (well actually comoving distance 350 Mpc/h), what are these angular separations in Mpc/h?

What noise levels would be expect just from shot noise?

How do we expect the slopes to compare?

I talked to David, Eric, Nic and Matt about this. They gave me some references to check out and also suggested that (just as a check) I set the redshifts of the 3d correlation function to all be the same, and then calculate the 3D and 2D, and compare them, they should basically be the same then, or at least proportional to each other.

David also suggested (as a way to figure out where my troubles are coming from.... to go back to the mocks, when the reconstruction was working)... and to then try applying the BOSS Geometry to these mocks and see if I can get the code to work on the mocks with the BOSS Masks. Then once that is working, swap in the BOSS data.

It's worth a try!

References to read:
Peebles 1980
Limber 1954

Still need to do the binning experiments that Alexia suggested. So much to do, so few hours in the day.

No comments:

Post a Comment