Determine if matrix is diagonal

`tf = isdiag(`

returns
logical `A`

)`1`

(`true`

) if `A`

is
a diagonal matrix;
otherwise, it returns logical `0`

(`false`

).

Use the

`diag`

function to produce diagonal matrices for which`isdiag`

returns logical`1`

(`true`

).The functions

`isdiag`

,`istriu`

, and`istril`

are special cases of the function`isbanded`

, which can perform all of the same tests with suitably defined upper and lower bandwidths. For example,`isdiag(A) == isbanded(A,0,0)`

.