  Computing $p \rightarrow q$ norm for matrices is a classical problem in
computational mathematics and power iteration is a well-known method for
computing $p \rightarrow q $ norm for a matrix with nonnegative entries. Here
we define an equivalent iteration method for computing $ S_p \rightarrow S_q $
norm for completely positive maps where $S_p$ is the Schatten $p$ norm. We
generalize almost all of the definitions, properties, lemmas, etc. in the
matrix setting to completely positive maps and prove an important theorem in
this setting.
