Proving Linearity of L:R(4)→R(4)

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Discussion Overview

The discussion revolves around proving the linearity of a linear transformation L defined from R(4) to R(4). Participants explore the requirements for linear transformations, including the necessary conditions to demonstrate linearity through specific calculations.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant expresses uncertainty about how to start proving the linearity of the transformation L.
  • Another participant emphasizes the importance of understanding the definition of a linear operator as a prerequisite for assistance.
  • It is suggested that the participant should write down the requirements for a linear transformation and perform the necessary calculations.
  • A participant acknowledges the need to prove that L(u+v) = L(u) + L(v) and L(c*u) = c*L(u), but struggles with setting it up correctly.
  • One participant attempts to demonstrate the linearity by substituting specific vectors u and v and calculating L(u+v) and L(c*u), leading to expressions that appear to confirm linearity.
  • Another participant corrects a notation error regarding the vectors used in the calculations, suggesting clearer conventions for representing vectors.
  • There is a discussion about the notation for matrices and whether MATLAB entry notation is acceptable for clarity.
  • A participant seeks verification of their calculations and signs after receiving help from others in the thread.

Areas of Agreement / Disagreement

Participants generally agree on the steps needed to prove linearity, but there is some confusion regarding notation and vector representation. The discussion remains unresolved as participants continue to seek clarification and verification of their calculations.

Contextual Notes

There are limitations in notation clarity and the representation of vectors, which may affect the understanding of the mathematical expressions involved in the proof.

jlucas134
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I need some help solving this...not even sure how to start...

Let L:R(4) goes to R(4) be the linear transformation defined by
-matlab notation, the value is a 4x1 column
L ( [ a b c d])=[ a-b
0
c-d
0 ]


Show directly L is linear.
 
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In order to get help, you should show some efforts.

What is the definition of a linear operator?
 
All I can say is "Just do it!"

Write down the requirements for a linear transformation, insert your L, and do the calculations!
 
Alright...

I am still trying to figure out this message board...
I forgot to include what I already know...

I know you have to prove that L(u+v)=L(u)+ L(v) and L(c*u)=c*L(u), but I don't understand how to set it up.

I tried to separate it into a1 and a2, but just get confused...

Do I have to place it in the standard matrix representation then solve?
 
still working with it...
if I set u=a1, b1, c1, d1 and v=a1, b1, c1, d1
set L(u+v)=(this is what I get)

[ (a1+a2)-(b1+b2)
0
(c1+c2)-(d1+d2)
0 ]

which equals L(u)+L(v)

for L(c*u)=c*L(u)

[c(a-b) c*0 c(c-d) c*0]
which converts to c[a-b 0 c-d 0] which breaks down to c*L(u)


Is the close?
 
Last edited:
That's exactly it.

(except that you said " I set u=a1, b1, c1, d1 and v=a1, b1, c1, d1" when you mean "I set u=a1, b1, c1, d1 and v=a2, b2, c2, d2". Doesn't your class or textbook have some convention for writing vectors- say (a, b, c, d) or <a, b, c, d> rather than just a, b, c, d which can be confusing?
 
ok...think i get it

When I first did it, it didn't look right...almost too simple to be correct. Thanks for correcting me with my notation.

my text does have a format but this doesn't support the large brackets required for a 4X1 matrix.

I will try to make the matrix a little more easier to read...

Would the notation for MATLAB entry suffice?
 
jlucas134 said:
my text does have a format but this doesn't support the large brackets required for a 4X1 matrix.

You can always write (a b c d)^T to represent a 4x1 matrix of you want.
 
Check me

Can someone verify my signs are correct for when I solved, with help from the board?
 

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