Given an
m
×
m
m \times m
symmetric nonnegative matrix
A
A
and a positive vector
R
=
(
r
1
,
⋯
,
r
m
)
R = ({r_1}, \cdots ,{r_m})
, necessary and sufficient conditions are obtained in order that there exist a diagonal matrix
D
D
with positive main diagonal such that DAD has row sum vector
R
R
.