Re: Matrix operations
On Jul 23, 6:20 pm, Jonathan Lee <jonathan.lee....@gmail.com> wrote:
On Jul 23, 12:59 pm, James Kanze <james.ka...@gmail.com> wrote:
On Jul 23, 3:18 pm, Jonathan Lee <jonathan.lee....@gmail.com> wrote:
Quite often these operators call their assignment
equivalents. For example
If this pattern is being used, then typically, you don't write
the operator* at all, but rather derive, e.g.:
class Matrix : public ArithmeticOperators<Matrix>
{
// ...
};
Where is this class from? Or is it just something of your
invention?
This particular version is my own, but I imagine all experienced
C++ programmers have something similar in their tool bag.
In any case, I guess it's an interesting idea.
But since the OP is asking about how to do operator
overloading, I would stand by my recommendation to do them
"manually".
Certainly. I was commenting on your proposal as to the pattern.
If you use the pattern of defining the <op>= operator first
(which you almost certainly wouldn't in a production matrix
class---this is an exercise), then you'd probably want to use
such a base class for the <op> operators. It's worth
mentionning the idiom, at the least, even if the poster needs to
know how to write the <op> operator without the base class
template, if only in order to be able to implement the base
class template.
(This is different than the question of how to write a
production quality matrix class---writing a production quality
matrix class needs mastery of a number of concepts which the
poster probably hasn't seen yet.)
And really.. how often do you define a new arithmetic
type?
It depends on the application domain; there's quite a few in my
current work. But even if you don't define new arithmetic
types, it's not rare to define a type which supports some
arithmetic operators.
Without seeing exactly what he means, it's hard to say. I don't
quite see how Vector could derive from Matrix.
As a 1-column or 1-row Matrix, I expect.
Which leads to the classical "is a cercle an ellipse" problem?
A vector has an additional invariant, compared to matrix.
Mathematically, there isn't much distinction between a matrix
and a vector as a special case of a matrix.
Yes, but the mathematical relationships don't always model by
inheritance---again, consider the "is a cercle an ellipse"
problem.
In particular, if he's doing any linear algebra,
setting things up this way seems reasonable.
Given the frequency of self-assignment, adding the check may
globally slow things down: you save a lot of time in
self-assignment, but you slow every assignment down by the time
it takes to make the check.
You're right, of course, but it also seems like a micro-optimization.
I use this all the time and neither gprof nor Valgrind has ever
scolded me for it.
It certainly doesn't make the program incorrect, if it were
otherwise correct. Practically speaking (and matrix may be an
exception to this general rule), if you think you need a check
for self alignment, the code is probably incorrect.
--
James Kanze