Linear maps
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Overview
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flowchart TD
A(Linear Maps <br/> linear transformation) --> D[Domain,Codomain]
A --> B[Mapping Rule: L]
B --> BA[Linear mapping?]
BA --> |check with|BAA[Linearity rules]
BA --> |quick check|BAB[Zero vector <br/>L0=0]
B --> BB[Matrix w.r.t. <br/> Standard Basis]
B --> BC[Matrix w.r.t. <br/>Non-Standard Basis]
BC --> |how to <br/>calculate map S <br/> w.r.t. basis:|BCA[Image of Basis <br/> using L]
BCA --> |use decomposition <br/> or LSE|BCB[to find coordinates. <br/> coefficients = coordinate. <br/> linear combination]
BCB --> |use coordinates <br/> vectors for|BCBA[Map S w.r.t <br/> new basis and insight <br/>about linear transformation]
B --> BD[Invertible Mapping]
BD --> |only possible <br/> if same dimension|BDA[inverse map of L: L^-1 <br/> = is unique and linear]
BDA --> |every reflection <br/>is invertibale|BDAA[L = L <br/> self-inverse]
BDA --> |if 2 x 2 matrix|BDAB[Use formular below]
A --> C[Affine Linear Maps]
C --> |Linear + shift|CA[Linear map + <br/>displacement vector w <br/> every linear map is <br/>affine map with w = 0 ]
CA --> |Image of zero vector|CB[displacement vector]
CA --> |used for example|CC[rotation around point other than origin]
Figure 1: A flow chart of concepts in linear maps
Python for calculating Coordinates
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import numpy as np
import scipy.linalg as la
A = np.array([
[-3,2,2],
[-3,1,3],
[-1,2,0]
])
#-----------Example first vector-------#
v_1 = np.array([
[2],
[1],
[2]
])
#---------Calculate Image of basis v_1---#
r_1 = A@v_1
#--------After repeating for all basis--#
S = np.hstack([v_1, v_2, v_3])
#' This gives us the coefficient matrix that is used as
#' LSE to calculate coordinates
#-------Solve each system----- #
#LSE of image of v_1
a_1 = la.solve(S, r_1)
#--------Final Matrix------#
B = np.hstack([a_1, a_2, a_3])
Mapping
What matrix size do we need if we want to map ?
- we would need a (3 x 2) matrix
Inverse of 2 x 2 Matrix
The denominator is the determinant of A.
Excerise 4.4
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