The spectral radius of an 
matrix 
with complex or real
elements and eigenvalues 
, ..., 
is
 |
i.e., the largest absolute value (or complex modulus) of its eigenvalues.
The spectral radius of a finite graph is defined as the largest absolute value of its graph spectrum, i.e., the largest absolute value of the graph eigenvalues (eigenvalues of the adjacency matrix) .
For a bounded operator 
on a nonzero complex Banach
space, the spectral radius is the maximum absolute
value of its operator spectrum. The spectral
radius formula gives 
.
Thus a quasinilpotent operator is one
with spectral radius zero.
