411 REFERENCE · Wikibooks
Math for Non-Geeks/Exercises Linear Maps
Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.
oben
We have compiled some tasks on linear maps here. The proof structures can help you to solve other similar tasks.
As a reminder, here is the definition of a linear map:
Linear map
Let be a mapping between the two vector spaces and . We call a linear map from to if the following two properties are satisfied:
ordered
Additivity: For all we have
Homogeneity: For all and we have
Proving linearity of a mapping
Linear maps from to
Linear map into a field
Let be defined by .
Show that the map is linear.
First you have to show the additivity and then homogeneity of the map. Additivity For this step, let
and .
Thus is additive.
Homogeneity Let and .
Thus is homogeneous and is linear.
Linear map from to
Lineare_Abbildung_von_3D_nach_2D
Show that the map with is linear.
You have to show that for and it holds true that
And you have to show that for , it holds true that
Aktuelles Ziel
Additivity
Aktuelles Ziel
Scaling
Linearity of the embedding
Show that for , the map is linear.
Let and , as well as . By definition of the map , we have that
So is linear.
aufgabe_linearität_R^2
Important special cases
aufgabe_identität_linear
aufgabe_nullabbildung_linear
Linear maps between function spaces
Mapping on a function space
Consider the function space of all functions from to , as well as the map
Show that is linear.
The operations on the function space are defined element-wise in each case.
That means: for , and we have that and .
In particular, this is true for , which implies
and
Thus, we have established linearity.
präkomposition_linear
folgenraum_abbildung_linear
Construction of a linear map from given values
Construction of a linear map
Let .
Further, consider .
Find a linear map with for all .
Hint: Use the principle of linear continuation.
We see that is a basis of , namely the standard basis.
According to the theorem of linear continuation, we can construct a linear map
defined by
Now we only have to check if is satisfied. It is true that , so
Thus, the condition is satisfied for each . The mapping is linear by definition, so we are done.
konstruktion_lin_Abb
Linear independence of two preimages
Let be a linear map and let and be two distinct vectors from , both mapped to a vector with . Prove that and are linearly independent.
We show that the two vectors cannot be linearly dependent. So assume that were linearly dependent. Then there would be a such that . We now map these two dependent vectors into the vector space using the linear map . This yields
Since by premise, , this is a contradiction and our assumption of linear dependence must be false.
Assume that and were linearly dependent. Then there would be a with and . Since the map is linear, it follows that
Thus
Since by assumption , we must have . But this contradicts our assumption . Thus, we get a contradiction to our assumption of linear dependence. So the vectors are linearly independent.
Exercises: Isomorphisms
aufgaben_isomorphismus
Exercises: Images
zuordnung_abbildung_bild
bild_einer_matrix
surjektivität_dimension
Exercises: Kernel
aufgabe_kern_bestimmen
kern_nilpotenter_endo
injektivität_und_dimension
unten