HI, I think it will be better if you posted this on R-help. A.K.? ----- Original Message ----- From: "hafida-06 at hotmail.fr" <hafida-06 at hotmail.fr> To: smartpink111 at yahoo.com Cc: Sent: Sunday, August 5, 2012 9:01 AM Subject: PROGRAMM MATRIX Hi can you please help me to programme this formula: g[ll']=i[ll']-sum from j=1 to k? c[lj]c[l'j]A[j]^-1 WHERE i[ll']= 1/n? sum from i=1 to n? z[il]z[il'] n,k,m? are given.? j=1...k,? ? l,l'=1...m,? it s complicate for me ; hope you can help me thank you a lot