Sigurdur Helgason is an Icelandic-American mathematician

Mathematician

A mathematician is a person whose primary area of study is the field of mathematics. Mathematicians are concerned with quantity, structure, space, and change....

 specializing in integral geometry

Integral geometry

In mathematics, integral geometry is the theory of measures on a geometrical space invariant under the symmetry group of that space. In more recent times, the meaning has been broadened to include a view of invariant transformations from the space of functions on one geometrical space to the...

 and its generalizations to symmetric spaces. He was born in Akureyri

Akureyri

Akureyri is a town in northern Iceland. It is Iceland's second largest urban area and fourth largest municipality ....

, Iceland. Since 1965, he has been a professor of mathematics at the Massachusetts Institute of Technology

Massachusetts Institute of Technology

The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...

. He was winner of the 1988 Leroy P. Steele Prize for Seminal Contributions for his books Groups and Geometric Analysis and Differential Geometry, Lie Groups and Symmetric Spaces. He has been a fellow of the American Academy of Arts and Sciences

American Academy of Arts and Sciences

The American Academy of Arts and Sciences is an independent policy research center that conducts multidisciplinary studies of complex and emerging problems. The Academy’s elected members are leaders in the academic disciplines, the arts, business, and public affairs.James Bowdoin, John Adams, and...

 since 1970.

Selected works

• Analysis on Lie group
  Lie group
  In mathematics, a Lie group is a group which is also a differentiable manifold, with the property that the group operations are compatible with the smooth structure...
  
  s and homogeneous space
  Homogeneous space
  In mathematics, particularly in the theories of Lie groups, algebraic groups and topological groups, a homogeneous space for a group G is a non-empty manifold or topological space X on which G acts continuously by symmetry in a transitive way. A special case of this is when the topological group,...
  
  s. AMS 1972
• Groups and geometric analysis
  Geometric analysis
  Geometric analysis is a mathematical discipline at the interface of differential geometry and differential equations. It includes both the use of geometrical methods in the study of partial differential equations , and the application of the theory of partial differential equations to geometry...
  
  : integral geometry
  Integral geometry
  In mathematics, integral geometry is the theory of measures on a geometrical space invariant under the symmetry group of that space. In more recent times, the meaning has been broadened to include a view of invariant transformations from the space of functions on one geometrical space to the...
  
  , invariant differential operator
  Differential operator
  In mathematics, a differential operator is an operator defined as a function of the differentiation operator. It is helpful, as a matter of notation first, to consider differentiation as an abstract operation, accepting a function and returning another .This article considers only linear operators,...
  
  s and spherical function
  Spherical function
  Spherical function can refer to* Spherical harmonics*Zonal spherical function...
  
  s. Academic Press 1984, AMS 1994
• Differential geometry, Lie groups and symmetric space
  Symmetric space
  A symmetric space is, in differential geometry and representation theory, a smooth manifold whose group of symmetries contains an "inversion symmetry" about every point...
  
  s. Academic Press 1978, 7. Auflage 1995
• Differential geometry and symmetric spaces. Academic Press 1962, AMS 2001
• The Radon Transform
  Radon transform
  thumb|right|Radon transform of the [[indicator function]] of two squares shown in the image below. Lighter regions indicate larger function values. Black indicates zero.thumb|right|Original function is equal to one on the white region and zero on the dark region....
  
  . Birkhäuser, 1980, 2. Auflage 1999
• Topics in harmonic analysis
  Harmonic analysis
  Harmonic analysis is the branch of mathematics that studies the representation of functions or signals as the superposition of basic waves. It investigates and generalizes the notions of Fourier series and Fourier transforms...
  
  on homogeneous spaces. Birkhäuser 1981