John Robert (Bob) Carruthers (1945-2009)
Bob graduated from St. Edmund Hall (Oxford) having completed his Part II year doing copper chemistry with Francis Rossotti. He worked for his D. Phil. with Keith Prout and Francis, and became interested in crystallography. For one of the materials he worked on, he observed 'When the diffraction pattern was indexed, it became apparent that the crystals were unlikely to be orthorhombic, as a strange set of absences were found'. The crystals were twinned, 'overlapped reflections were arbitrarily assigned half the measured intensity until a program was written which would include both components in the least squares'. 'As there was not sufficient memory, it was necessary to rewrite the program in machine language'. Machine languages are basic to the electronics of the computer, and the programmer has the power and the responsibility of working hands-on with every memory location. So began Bob’s life with computers, and his exceedingly productive partnership with John Rollett.
In 1969, Bob was awarded a fellowship from the Accademia Nazionale dei Lincei and the Royal Society, allowing him to work in Rome with Riccardo Spagna re-implementing the Rollett AUTOCODES symbolic language in FORTRAN. This program included features such as rigid-body constraints and some of the underlying data-structure can still be found in CAOS (Cerrini S. & Spagna R. 1977) crystallographic software for a mini computer.
Returning to Oxford, he worked with Rollet and Prout, re-writing the program from scratch. This new program, CRYSTALS, could handle up to 9 twinned components and had a good range of restraints (including facilities now often called SIMU and DELU). Perhaps the most novel feature was 'user-defined restraints', in which users could define their own equation of restraint as part of the input data, which was then analytically differentiated by CRYSTALS. The equation parser and differentiating engine were all written in beautiful FORTRAN and are still working, largely unmodified, in the current version of CRYSTALS. Bob's attitude toward programming combined a meticulous attention to detail with a far-reaching ability to plan on an expansive scale.
After his Postdoc, Bob started writing data-archiving software for Oxford U. Computing Service. However, he continued to work on CRYSTALS whenever he could and completely re-wrote the underlying data management for a third time when the university upgraded its mainframe to an International Computers Limited (ICL) 2980.
Around 1979, Bob went to work for Control Data Corporation, implementing meteorology programs on supercomputers. He spent most of his career implementing very large FORTRAN program systems and in recent years modernizing massive legacy packages. Weather forecasting profited from his work, but there is no doubt that crystallography lost an outstanding programmer.
When not working with computers, Bob was a dependable drinking companion and a formidable bar billiards enthusiast. Some of us still remember Bob and George Sheldrick, with other young crystallographers, trying to drink the bar dry at ECM 4 in Oxford in 1977. His brilliance as a scientist did not spoil his personality - he was always modest, amiable and good fun.David Watkin