fos MAY 3 1965

NORTHWESTERN UNIVERSITY

EVANSTON, ILLINOIS 60201

THE TECHNOLOGICAL INSTITUTE . -
DEPARTMENT OF MATERIALS SCIENCE April 27, 1965

N Ae

Professor J. Lederberg

Executive

Department of Genetics

School of Medicine

Stanford University Medical Center
Palo Alto, California

Dear Dr. Lederberg:

Please excuse the delay in my reply to your letter about our com-
puter methods with metallic alloys; I wanted to take the time to
read the paper that you very kindly included.

May I be so bold as to make one suggestion. The field of image
algebra or Patterson functions, as it is sometimes called by the
experimental diffraction people, might prove very interesting
with regard to the schemes you are trying to set up.

vaPldD Yd

Unfortunately, Mr. Gehlen has already committed himself to a job
at Battelle Memorial Institute. We will be glad to provide you
with details of our program. Unfortunately this will not appear
in print until July 19th (in Fhysical Review), but we will be glad
if someone from your group would like to visit and go over the
actual details of what is going on. I do not at the present time
have a preprint. Essentially what we are doing is this. A
number of atoms is placed in the computer - up to 16,000 - and the
computer chooses an A atom and a B atom at random and interchanges
them, if this interchange brings one close to an experimentally
measured probability. This probability is the average over all
atoms of the occupation at a vector distance from the A atom and
the information is available for a variety of vector distances.
Thus the computer arranges the atoms to satisfy this average and
we can look and see just how many different structures can arise
with a given average and the actual structures that are involved.

Sincerely yours,

IB Gln

JBC: cn Jd. B. Cohen
Associate Professor