Biconvex optimization

Biconvex optimization is a generalization of convex optimization where the objective function and the constraint set can be biconvex. There are methods that can find the global optimum of these problems.[1][2]

A set B X × Y {\displaystyle B\subset X\times Y} is called a biconvex set on X × Y {\displaystyle X\times Y} if for every fixed y Y {\displaystyle y\in Y} , B y = { x X : ( x , y ) B } {\displaystyle B_{y}=\{x\in X:(x,y)\in B\}} is a convex set in X {\displaystyle X} and for every fixed x X {\displaystyle x\in X} , B x = { y Y : ( x , y ) B } {\displaystyle B_{x}=\{y\in Y:(x,y)\in B\}} is a convex set in Y {\displaystyle Y} .

A function f ( x , y ) : B R {\displaystyle f(x,y):B\to \mathbb {R} } is called a biconvex function if fixing x {\displaystyle x} , f x ( y ) = f ( x , y ) {\displaystyle f_{x}(y)=f(x,y)} is convex over Y {\displaystyle Y} and fixing y {\displaystyle y} , f y ( x ) = f ( x , y ) {\displaystyle f_{y}(x)=f(x,y)} is convex over X {\displaystyle X} .

A common practice for solving a biconvex problem (which does not guarantee global optimality of the solution) is alternatively updating x , y {\displaystyle x,y} by fixing one of them and solving the corresponding convex optimization problem.[1]

The generalization to functions of more than two arguments is called a block multi-convex function. A function f ( x 1 , , x K ) R {\displaystyle f(x_{1},\ldots ,x_{K})\to \mathbb {R} } is block multi-convex iff it is convex with respect to each of the individual arguments while holding all others fixed.[3]

References

  1. ^ a b Gorski, Jochen; Pfeuffer, Frank; Klamroth, Kathrin (22 June 2007). "Biconvex sets and optimization with biconvex functions: a survey and extensions" (PDF). Mathematical Methods of Operations Research. 66 (3): 373–407. doi:10.1007/s00186-007-0161-1. S2CID 15900842.
  2. ^ Floudas, Christodoulos A. (2000). Deterministic global optimization : theory, methods, and applications. Dordrecht [u.a.]: Kluwer Academic Publ. ISBN 978-0-7923-6014-8.
  3. ^ Chen, Caihua (2016). ""The direct extension of ADMM for multi-block convex minimization problems is not necessarily convergent"". Mathematical Programming. 155 (1–2): 57–59. doi:10.1007/s10107-014-0826-5. S2CID 5646309.
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