spcompack — converts a compressed adjacency representation

- xadj
integer vector of length (n+1).

- xlindx
integer vector of length n+1 (pointers).

- lindx
integer vector

- adjncy
integer vector

Utility fonction spcompak is used to convert a compressed adjacency representation into standard adjacency representation.

// A is the sparse matrix: A=[1,0,0,0,0,0,0; 0,1,0,0,0,0,0; 0,0,1,0,0,0,0; 0,0,1,1,0,0,0; 0,0,1,1,1,0,0; 0,0,1,1,0,1,0; 0,0,1,1,0,1,1]; A=sparse(A); //For this matrix, the standard adjacency representation is given by: xadj=[1,2,3,8,12,13,15,16]; adjncy=[1, 2, 3,4,5,6,7, 4,5,6,7, 5, 6,7, 7]; //(see sp2adj). // increments in vector xadj give the number of non zero entries in each column // ie there is 2-1=1 entry in the column 1 // there is 3-2=1 entry in the column 2 // there are 8-3=5 entries in the column 3 // 12-8=4 4 //etc //The row index of these entries is given by the adjncy vector // for instance, // adjncy (3:7)=adjncy(xadj(3):xadj(4)-1)=[3,4,5,6,7] // says that the 5=xadj(4)-xadj(3) entries in column 3 have row // indices 3,4,5,6,7. //In the compact representation, the repeated sequences in adjncy //are eliminated. //Here in adjncy the sequences 4,5,6,7 and 7 are eliminated. //The standard structure (xadj,adjncy) takes the compressed form (lindx,xlindx) lindx=[1, 2, 3,4,5,6,7, 5, 6,7]; xlindx=[1,2,3,8,9,11]; //(Columns 4 and 7 of A are eliminated). //A can be reconstructed from (xadj,xlindx,lindx). [xadj,adjncy,anz]= sp2adj(A); adjncy-spcompack(xadj,xlindx,lindx)