Roger Barrett's memorial service

 On Friday, a memorial service was held for Roger Barrett, who died in January It was a service organised and run by his family.  I listened and shed a few tears at the loving reminiscences by his siblings and children, who recounted aspects of his life, starting from his childhood in Southern Rhodesia (now Zimbabwe) where his parents taught at a boarding school, to his University days in Oxford, his early career with a couple of positionsi in the US, and his life in Guildford.  It concentrated, of course, on the family reminiscences and on what Roger meant to the people present. 

Ron Johnson, emeritus professor in our Department, led the part of the proceedings talking about Roger's professional life at Surrey, which took up the greater part of Roger's career, talking of his pioneering use of computing in calculations of phase shifts in nuclear scattering.  

I knew something of Roger's work at Surrey, but little of his family life.  I also had no idea that he had worked at Columbia University as a post-doc of C.-S. Wu, the Chinese-American physicist who should have won two Nobel prizes (one for the experimental proof that parity is not conserved, and one for observation of quantum entanglement in photons).  A quick search reveals papers from Roger from after he arrived at Surrey, still collaborating with C.-S. Wu, and with Nobel laureate James Rainwater. 

Roger's family spoke endearingly of his nerdish qualities.  The one I liked best was that when he microwaved coffee, he always put the cup in with the handle pointing to the open door, then ensured that he heated it up for a multiple of 11 seconds, as that was the period of rotation of the microwave plate, ensuring that the handle was in the right place after heating!

His last few years sounded physically brutal, through the recurrence of a thought-beaten cander which had travelled to his spine causing so much destruction that he was immobile for four years.  Apparently, he retained good humour, which seemed a great comfort to his family.  RIP Roger. 

 

NuSec

I'm at the Institute of Physics buildings in London today for.a workshop on Nuclear Security, being the annual workshop of the NuSec nuclear security network.  The work being presented concentrates on detection of radiation, which is an area I have not worked directly on, but is a key part of nuclear physics, and it's interesting in its own right, with particular extra interest in today's workshop coming from its applications.  

 As ever, there are lots of contrived acronyms to be spotted.  Here's one - PReTSL - in a talk by Robin Smith from Sheffield Hallam University.

January book: Wong's "Introduction To Classical And Quantum Computing"

 It's nearly the end of February, so high time I wrote up January's book.  This is Introduction to Classical and Quantum Computing by Thomas Wong.  I think I first came across it, or at least really took a good look at it, when a colleague recommended it as a text for our new Applied Quantum Computing MSc. 

The author, Thomas Wong, has generously made the book freely downloadable from his website,  Having decided to make use of it for teaching, I shelled out for a copy at the rather cheap price (for a science textbook) of £11.76 for a print-on-demand paperback.  Unlike December's book, which was also print-on-demand,  Wong's book is well-formatted for printing.

I really like this book.  It does a difficult job - introducing enough classical computing, quantum mechanics and quantum computing - kinda three different and disparate topics despite the similar sounding names - and does a good job of it.  It's become my go-to textbook for the course I teach in quantum algorithms, though it is too basic for my masters-only quantum simulation class.  

Wong updates the book and produces more editions when the need arises.  I have found a few little typos in it as I have been working through derivations in preparation for teaching, and I keep them marked up in a copy that I will send to Wong in case he wants to make any more updates

Screenshot below a sample marked-up bit where I saw a typo.  That circled ket-bra should be a bra-ket

ascii2spec.f90

Following up the last post, where I documented the function which maps the ASCII representation of the letters s, p, d, f, g, h, i, j, k, to the numbers 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,  I complete the job today where I mentioned that one reason to do this mapping is to allow translation between the letters and the numbers in a computer language in a mathematical way.

Before coding up the polynomial function which does the mapping, it is helpful / necessary to re-express it in a different form that is not so prone to rounding errors.  Such a thing can be done by writting the polynomial in Horner form, which results in 

 

Here, then is a Fortran code which uses this form of the polynomial, which it can evaluate without error (with the use of double precision intermediary values).  If you want to use it, you can use the module a2s.  A sample code showing that it works is included in the snippet below

! take the ascii value for a spectroscopic identifier (s, p, d, f etc)
! and return the corresponding l value (0, 1, 2, ) etc.

module a2s
  contains
  function ascii2spec(x)
    implicit none
    integer, parameter :: rk=selected_real_kind(16)
    integer :: ascii2spec
    integer :: x
    
    ascii2spec= NINT(4.726949979612458e10_rk + x*(-3.5777271221003e9_rk + & 
         x*(1.184502721723563e8_rk + x*(-2.2405263573528733e6_rk + &
         x*(26482.917002197904_rk + &
         x*(-200.30039731359176_rk + &
         x*(0.946665443609888_rk + &
         (-0.002556173250617695_rk + (47*x)/1.5567552e7_rk)*x)))))))
  end function ascii2spec
end module a2s

program a2s_test
  use a2s
  integer, parameter :: rk=selected_real_kind(16)
  integer :: x
  
  print *,"s",ascii2spec(iachar("s"))
  print *,"p",ascii2spec(iachar("p"))
  print *,"d",ascii2spec(iachar("d"))
  print *,"f",ascii2spec(iachar("f"))
  print *,"g",ascii2spec(iachar("g"))
  print *,"h",ascii2spec(iachar("h"))
  print *,"i",ascii2spec(iachar("i"))
  print *,"j",ascii2spec(iachar("j"))
  print *,"k",ascii2spec(iachar("k"))

end program a2s_test