[SciPy-Dev] linalg.toeplitz and ticker #667

[Warren Weckesser]

Warren Weckesser wrote:
> I am going to update linalg.toeplitz to fix the problem reported in
> ticket #667, but I have some questions about the desired behavior of
> the function when either `c` (the first column) or `r` (the first row)
> is complex.  The docstring does not say anything about complex values,
> but the code does some undocumented and unexpected things in this
> case, one example of which is the bug reported in the ticket #667.
>
> I would like to fix this, but I would first like opinions on exactly
> how it *should* handle complex arguments.  I *think* the idea is that
> if `c` is complex and `r` is not given, then a Hermitian Toeplitz
> matrix is created.  Is that correct?  Note that this requires that
> c[0] be real, since c[0] is the value that will be in the diagonal of
> the matrix.
>
> While I am fixing this, I would like to remove the printed warning
> that occurs when r[0] != c[0].  I would like to change this to raise
> a ValueError--that is, adopt the philosophy that either the arguments
> are correct (and the code handles them as [not yet, but soon to be]
> documented in the docstring, with no warnings needed), or the
> arguments are wrong and an exception should be raised.
>
> This means that when `r` is not given, an exception would be raised
> if c[0] is not real.
>
> A very different way to handle the case of `r` not being given is to
> assume it means a square matrix should be created with r[1:] = 0
> (i.e. zeros in all the upper off-diagonals).  This avoids the whole
> issue of complex numbers and conjugates, but it is also a more
> drastic change.
>
>   

By the way, that is how linalg.hankel handles the case where `r` is not 
given.


Warren