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Nov
3
awarded  Popular Question
Nov
2
awarded  Popular Question
Oct
29
comment Completely baffled by this question involving putting matrices in matrices
Ahh thanks. I was trying to concoct $R$ using multiplications and sums of things involving $P$ and $Q$... Also, is there some trick to intuitively "getting" matrix multiplication? Like, I can calculate it, but I can never eyeball even a very high-level picture of what happens to various properties when you multiply two matrices.
Oct
29
accepted Completely baffled by this question involving putting matrices in matrices
Oct
29
comment Completely baffled by this question involving putting matrices in matrices
C is $m\times n$.
Oct
29
asked Completely baffled by this question involving putting matrices in matrices
Oct
10
accepted Having trouble understanding this proposition from my textbook.
Oct
5
comment Having trouble understanding this proposition from my textbook.
But can't $\vec{y}$ be of the wrong dimension to multiply by $A$? After all, it is formed with $A_B$, which has different dimensions from $A$.
Oct
5
asked Having trouble understanding this proposition from my textbook.
Oct
1
accepted Is matrix multiplication by an invertible matrix one-to-one and onto?
Oct
1
comment Is matrix multiplication by an invertible matrix one-to-one and onto?
What about $f(X)=XA$?
Oct
1
comment Is matrix multiplication by an invertible matrix one-to-one and onto?
Yes, but how about the "inverse" multiplication? Also, $X$ is a matrix, not a vector.
Oct
1
asked Is matrix multiplication by an invertible matrix one-to-one and onto?
Sep
18
comment Confusing DE concept question
Define "reduced".
Sep
17
awarded  Citizen Patrol
Sep
12
comment Are there “numbers” with infinite number of digits (to the left) and are they useful?
Maybe start with something simple: how would you convert such a number from decimal to binary for example?
Sep
10
accepted Proving that similar matrices have identical ranks
Sep
9
asked Proving that similar matrices have identical ranks
Sep
5
comment Why do you add +1 in counting test questions?
It's sad to see "add 1 to counting test problems" being taught as one of those "rules"...
Aug
25
comment Paradoxes without self-reference?
The liar paradox and also the "set of all sets" paradox seem to be true paradoxes, revealing incompleteness of certain systems of logic or set theory.