Showing null space and range are invariant

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SUMMARY

The discussion focuses on proving that the null space and range of a linear operator T are invariant under another linear operator S when both operators commute (ST = TS). Participants emphasize the need to demonstrate that if an element y is in the range of T, then S(y) remains in the range of T. The proof involves showing that for any x in the null space of T, ST(x) = 0, confirming that the null space is invariant under S. The key conclusion is that both the null space and range of T are preserved when acted upon by S.

PREREQUISITES
  • Understanding of vector spaces and linear operators
  • Knowledge of null space and range concepts
  • Familiarity with the properties of commutative operations in linear algebra
  • Basic skills in mathematical proof techniques
NEXT STEPS
  • Study the properties of linear operators in vector spaces
  • Learn about the implications of operator commutativity in linear algebra
  • Explore examples of null space and range invariance in practical applications
  • Investigate advanced topics such as eigenvalues and eigenvectors related to linear operators
USEFUL FOR

Mathematics students, educators, and researchers in linear algebra, particularly those focusing on operator theory and vector space properties.

adottree
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If V is any vector space and S and T are linear operators on V such that ST=TS show that the null space and the range of T are invariant under S.

I think I need to begin by taking an element of the range of T and having S act on it and show that it stays in V? Can you help get me started?
 
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adottree said:
If V is any vector space and S and T are linear operators on V such that ST=TS show that the null space and the range of T are invariant under S.

I think I need to begin by taking an element of the range of T and having S act on it and show that it stays in V? Can you help get me started?

Showing that it stays in V is not quite what you want to do. You want to show that every element in the range of T remains in the range of T when acted upon by S.

So say, t is an element in the range of T, what can you say about this element?
 
adottree said:
If V is any vector space and S and T are linear operators on V such that ST=TS show that the null space and the range of T are invariant under S.

I think I need to begin by taking an element of the range of T and having S act on it and show that it stays in V? Can you help get me started?
If x is in the null space of T, then T(x)= 0. Therefore, ST(x)= ?. And so T(S(x))= ?

If y is in the range of T, then there exist x such that T(x)= y. So S(T(x))= S(y). But that is equal to T(S(x)). So S(y) is in ?
 

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