matlab code for preconditioner P

Matlab code for preconditioner P Given a linear equation of the form Ax=b For example where A=[6 2 4;3 4 3; 3 1 2] and b=[26 19 13]' A =

     6     2     4
     3     4     3
     3     1     2
b =

    26
    19
    13
I need matlab code for a preconditional  P such that 
P=
     1    -2/A(2,2)   0
    0     1    -3/A(3,3)
    0    0     1

P= 1 -0.5 0 0 1 -1.5 0 0 1

2. I need a matlab code to convert the main diagonal of a matrix to one for example A= 6 2 4 3 4 3 3 1 2 F== 1 2/6 4/6 3/4 1 3/4 3/2 1/2 1

Answer 1

[Steven Lord]

Replace "a22" in your expression for P with "A(2, 2)" [and similarly for a33] and add in some square brackets, maybe some semicolons and/or commas to make it explicit what matrix you're creating, and you should be all set.

For part 2, I'll just give you a hint: look at the diag function.