Updating inverses in matrix analysis of structures

We deal with the problem of updating inverses, Several methods which allow calculating the inverse of a matrix when one or several rows (columns) are changed, or one or several rows and the same number of columns are added or removed are given. They are based on a method for calculating inverses giv en by Jubete and Castillo, which uses the concept of orthogonal sets, and l ead to a considerable saving in computational power. The methods are ideal for being used in the design process of structures, where stiffness matrice s are sequentially modified by simply changing rows (columns), and adding o r removing rows and columns, as the result of modifying the geometric or st ructural characteristics of its pieces, the structure's degrees of freedom, and/or the boundary conditions. Some examples of simple structures are giv en to illustrate the methodology. Finally, a discussion about its practical application and some conclusions and recommendations are given. (C) 1998 J ohn Wiley & Sons, Ltd.