Circuit lower bounds and linear codes

In 1977, Valiant proposed a graph-theoretical method for proving lower bounds on algebraic circuits with gates computing linear functions. He used this method to reduce the problem of proving lower bounds on circuits with linear gates to proving lower bounds on the rigidity of a matrix, a notion that he introduced in that paper. The largest lower bound for an explicitly given matrix is due to J. Friedman, who proved a lower bound on the rigidity of the generator matrices of error-correcting codes over finite fields. He showed that the proof can be interpreted as a bound on a certain parameter defined for all linear spaces of finite dimension. In this note, we define another parameter that can be used to prove lower bounds on circuits with linear gates. Our parameter may be larger than Friedman's, and it seems incomparable with rigidity, hence it may be easier to prove a lower bound using this notion. Bibliography: 14 titles. © 2006 Springer Science+Business Media, Inc.