Issue #12356 has been updated by jeremyevans0 (Jeremy Evans).

Assignee set to marcandre (Marc-Andre Lafortune)
Status changed from Open to Assigned

I don't think this is a bug, but I'll let marcandre make the determination.  `Vector` can't be multipled with `Vector`, you get an error.  You can multiple a `Vector` by a `Matrix` and vice-versa by design, and `Vector#covector` returns a `Matrix`.  You can multiple a `Matrix` by a `Matrix` only if the column_count of the receiver is the row count of the argument.

Whether `Vector` is good design or bad design I'm not going to speculate on.  However, you could consider using NMatrix (https://rubygems.org/gems/nmatrix), as that represents vectors as matrices.

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Bug #12356: Vector covector incorrect multiplication with another vector.
https://bugs.ruby-lang.org/issues/12356#change-80949

* Author: edmorte (Rafael Silva)
* Status: Assigned
* 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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