[ruby-core:94568] [Ruby master Bug#12356] Vector covector incorrect multiplication with another vector.

[ruby-core@marc-andre.ca]

Issue #12356 has been updated by marcandre (Marc-Andre Lafortune).

Status changed from Assigned to Rejected

Thanks Jeremy for updating this issue. I double checked and never received the original email notification...

> `Vector` does not have distinction between row and column, there's no column vector notion in the language.

Actually, in the library `Vector` is a column vector. You can see this for example with:

```
Vector[1, 2].to_matrix # => Matrix[[1], [2]]
```

So I believe that it is correct that `v.covector * v` or `v * v.covector` returns some result while other combinations should raise.

I'll close this but will reopen if there's more discussion to be had.


----------------------------------------
Bug #12356: Vector covector incorrect multiplication with another vector.
https://bugs.ruby-lang.org/issues/12356#change-81025

* Author: edmorte (Rafael Silva)
* Status: Rejected
* Priority: Normal
* Assignee: marcandre (Marc-Andre Lafortune)
* Target version: 
* ruby -v: ruby 2.2.4p230 (2015-12-16 revision 53155) [x86_64-linux]
* Backport: 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
----------------------------------------
Version 2.2.4

v1	=	Vector[2,3,4]
v2	=	Vector[4,5,6]
v1.covector.row_size      #1
v1.covector.column_size   #3
v2.covector.row_size      #1
v2.covector.column_size   #3

Vector does not have distinction between row and column, there's no column vector notion in the language.

v1 * v2.covector #Matrix[[8,10,12],[12,15,18],[16,20,24]]
# Should be illegal. But works like if v2.covector is transposed / column vector which it's clearly not.

v1.covector * v2.covector #ExceptionForMatrix::ErrDimensionMismatch: Matrix dimension mismatch
# Expected

v1 * v2 #ExceptionForMatrix::ErrOperationNotDefined: Operation(*) can't be defined: Vector op Vector
# No comments, see my observation below.

v1.covector * v2 #Vector[47]
#Again covector treated like transposed / column vector.

Personal observation: Terrible choice to represent Vector like an Array, Vector should be a shortcut to Matrix.



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