Le 08/07/2011 08:44, Sebastien Brisard a écrit :
Hi everyone,
well the message below did not raise much of an interest... My apology, I
forgot to quote [math] in the title.
Sorry, I forgot to reply in a timely fashion.
Anyway, I have a new proposal regarding this issue. I do not know what your
view on the subject is, but I tend to think that exceptions should return
references and not deep copies of the objects that caused these exceptions to
be raised. This facilitates debugging (I guess), and also helps identify the
exact origin of the problem, without having to specialize the exception. As an
Yes, exception are targeted towards handling of ... exceptional cases,
not heavy duty use during normal production. As such, they should not be
over-optimized for speed.
example, Conjugate Gradient requires positive definiteness of both matrix (a)
and preconditioner (m). If a NonPositiveDefiniteLinearOperatorException is
caught, then I can simply test
a == e.getOffendingLinearOperator()
or
m = e.getOffendingLinearOperator()
Now, coming to offending vectors, the issue is that these can either be
instances of RealVector, or double[]. So, what type should be returned by
getOffendingVector()?
I propose to have the exceptions return a reference to the RealVector. If the
exception was raised with a double[], then the returned RealVector will
actually be an instance of ArrayRealVector, with a reference to the initial
double[]. All this is to be clearly specified in the javadoc. Does that sound
like a viable option?
I would go to the natural type we get when building the exception. If we
may build the exception from both types, then I would select RealVector.
We do not intend to perform large processing on elements, but we want to
display them and I think we do have formatting for vectors.
best regards,
Luc
I'll attach the corresponding files to the JIRA issue, if you want to have a
more precise idea of what I'm talking about.
Thanks in advance for your comments,
Sebastien
Good morning,
my proposal for the implementation of linear iterative solvers (JIRA
MATH-581)
has raised some comments from Gilles and Luc, but I think no consensus has
been reached on one issue raised by Gilles. Before submitting a new version
of
the corresponding classes, I'd like to make a new proposal.
Here is the thing. I have defined two exceptions, namely
- NonSelfAdjointLinearOperatorException
- NonPositiveDefiniteLinearOperatorException,
the latter being typically raised when a vector x is found, such as x'.A.x
<=
0, where A is the linear operator under consideration.
Now, the constructor of this exception takes as input A and x (which I call
the "offending vector"). There is a method to return a reference to A (which
is a RealLinearOperator), and a method to return a deep copy of x, the
reason
for this is that x can either be a double[], or a RealVector.
I agree with Gilles, for debugging purposes, it would probably be better to
be
able to trace the offending vector, hence to have the exception return a
reference to this offending vector. But this is just not possible, since
there
is no unique type for this vector. Gilles pointed out that there is the
method
getData() in RealVector which would do the job, but there is no requirement
in
the contract of this method for this to be a shallow/deep copy. Is this a
concern ? If not, then I could change the current method
void copyOffendingVector(final double[] x)
(where x is modified)
into
double[] getOffendingVector()
but we would lose the track of the actual object which first raised the
exception.
Another option would be to have the method getOffendingVector() return an
Object, and try to cast it to a RealVector or a double[] when catching the
exception. Not too sure it's good practice to return Objects, though.
I'm looking forward to reading your comments, and will update the sources
accordingly.
Sebastien
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