When creating a matrix with only one zero dimension, we end up with a
matrix with a total size of zero, but a non-zero stride for elements.
While such a matrix can never actually have any elements, we need to be
careful with how we use the pointer associated with it.
Since such a pointer will always be dangling, it can never be used with `ptr.offset`,
which requires that the pointer be in-bounds or one passed the end of an
allocation. Violating this results in undefined behavior.
This commit adds in checks before the uses of `ptr.offset`. If we ever
need to offset from a pointer when our actual allocation size is zero,
we skip offsetting, and return the original pointer. This is fine
because any actual use of the original or offsetted pointer would
already be undefined behavior - we shoul never be trying to dereference
the pointer associated with a zero-size matrix.
This issue was caught be running `cargo miri test` on the project.
The added method `Vector::axcpy` generalises `Vector::gemv` to
noncommutative cases since it allows us to write for `gemv`
`self.axcpy(alpha, &col2, val, beta)`, instead the usual
`self.axpy(alpha * val, &col2, beta)`. Hence, `axcpy` preserves the
order of scalar multiplication which is important for applications where
commutativity is not guaranteed (e.g., matrices of quaternions, etc.).
This commmit also removes helpers `array_axpy` and `array_ax`, and
replaces them with `array_axcpy` and `array_axc` respectively, which
like above preserve the order of scalar multiplication.
Finally, `Vector::axpy` is preserved, however, now expressed in terms of
`Vector::axcpy` like so:
```
self.axcpy(alpha * val, &col2, beta)
```
The eigenvalue problem is solved in two different method that use different methods
to calculate the discriminant of the solution to the quadratic equation.
Use the method whose computation is considered more stable.
* Bumped rand version to 0.7
* Added dependency to rand_distr
* Bumped quickcheck version to 0.9 (because of rand)
* Bumped rand_xorshift version to 0.2
