Archive for July 8, 2019

O Grande Amor – Getz & Gilberto

Posted in Jazz with tags , , , , on July 8, 2019 by telescoper

There was a time in the 1960s when the Bossa Nova seemed to be everywhere and no one person did more to stimulate the growth of this uniquely Brazilian musical form than singer, guitarist and composer João Gilberto, who passed away on Saturday 6th July at the age of 88. It was Gilberto’s collaboration with tenor saxophonist Stan Getz (and, on some tracks, his wife Astrud Gilberto) on the award-winning album Getz/Gilberto that made the Bossa Nova go global, penetrating not only the world of jazz but the much wider cultural sphere including pop and film music. The most famous track from Getz/Gilberto is undoubtedly The Girl From Ipanema which was a smash hit around the globe in 1964, but my own favourite number from that album is this, with lovely playing by Stan Getz and characteristically understated, almost whispered vocal by João Gilberto himself.

Rest in Peace João Gilberto (1931-2019)

Cosmology with the Minimal Spanning Tree

Posted in The Universe and Stuff with tags , , , , , , on July 8, 2019 by telescoper

There’s a nice paper on the arXiv (by Naidoo et al) with the abstract:

The code mentioned at the end can be found here.

The appearance of this paper gives me an excuse to mention that I actually wrote a paper (with Russell Pearson) on the use of the Minimal (or Minimum) Spanning Tree (MST) to analyze galaxy clustering way back in 1995.

Here’s how we described the Minimal Spanning Tree in that old paper:

Strictly speaking , we used the Euclidean Minimum Spanning Tree in which the total length of the lines connecting a set of points in a tree is minimized. In general cases a weight can be assigned to each link that is not necessarily defined simply by the length. Here is visual illustration (which I think we drew by hand!)

You can think of the MST as a sort of pre-processing technique which accentuates linear features in a point process that might otherwise get lost in shot noise. Once one has a tree (pruned and/or separated as necessary) one can then extract various statistical properties in order to quantify the pattern present.

Way back in 1995 there were far fewer datasets available to which to apply this method and it didn’t catch on at the time. Now, with  ever-increasing availability of spectroscopic redshift surveys maybe its time has come at last! I look forward to playing with the Python code in due course!