Praktische Aspekte der Informatik

Transcription

1 Praktische Aspekte der Informatik Moritz Mühlhausen Prof. Marcus Magnor

2 Matlab Prototyping and designing new algorithms

3 Further Reading Warning! The following slides are meant to give you a very superficial introduction. If you want to learn more, have a look at:

4 Outline Introduction Matrices Plotting Programming Language

5 Introduction Benefits Drawbacks A large and widely used toolbox of numeric and image functions. A great tool for prototyping and developing new algorithms. It can be slow. You need a license. Untyped variables. A lot of high-level features. You can link C/C++/cuda!

6 Introduction

7 Outline Introduction Matrices Plotting Programming Language

8 Matrices Variables and Data Types will be very familiar to you. char, int8, uint8, int64, uint64, single, double, Matlab treats all variables as matrices. Vectors are matrices with only one row/column. Values are matrices with only one entry. >> M = [1,2,3; 4,5,6; 7,8,9] M =

9 Matrices >> M = [1,2,3; 4,5,6; 7,8,9] M = >> M_sub = M(1:2,:) M_sub =

10 Matrices j:k is the same as [j,j+1,...,k] is empty if j > k j:i:k is the same as [j,j+i,j+2i,..,k] is empty if i > 0 and j > k or if i < 0 and j < k. A(:,j) is the j-th column of A. A(i,:) is the i-th row of A. A(:,:) is the equivalent two-dimensional array. For matrices this is A. A(j:k) A(:,j:k) is A(j), A(j+1),...,A(k). is A(:,j), A(:,j+1),...,A(:,k). A(:,:,k) is the k-th page of three-dimensional array A. A(i,j,k,:) is a vector in a four-dimensional array A. A(:) is all the elements of A, as a single column. On the left side of an assignment statement, A(:) fills A.

11 Matrices X = M Transposed matrix M X = inv(m) Inverse of an n n matrix M X = det(m) Determinant of M [X,D] = eig(m) Eigenvalues and Eigenvectors of M [r,c] = size(m) Size of M [Q,R] = qr(m) QR decomposition of M

12 Outline Introduction Matrices Plotting Programming Language

13 Plotting Matlab can also quickly plot your data >> X = [1,4,6,8]; >> Y = [7,3,5,2]; >> plot(x,y) You can also plot a single vector, Matlab will just use it s indices >> V = [6,4,8,2]; >> plot(v)

14 Plotting Bar Charts >> V = [ ]; >> bar(v) Scatter Plots >> X = rand(1,100); >> Y = rand(1,100); >> plot(x,y,'*')

15 Outline Introduction Matrices Plotting Programming Language

16 Programming Language For-Loop Conditional if a == b, elseif a > b else end for i = 1:8 for j = {1:4,8,15} end end While-Loop while i < N end

17 Programming Language You can often avoid simple loops for i = 1:10000 end x(i) = sin(i); by doing something like this n = 1:10000; x = sin(n);

18 Programming Language You can also create reusable scripts and functions imagedenoisetest.m image = imread('padi.png'); % RGB image redchannel = image(:,:,1); % extract the first channel redchannel = wiener2(redchannel,[5,5]); % denoising function disp('image denoised!'); imshow(redchannel); % show the result >> imagedenoisetest Image denoised!

19 Programming Language You can also create reusable scripts and functions functiontest.m function [denoisedimage] = functiontest(imagename) image = imread(imagename); % RGB image denoisedimage = image(:,:,1); % extract the first channel denoisedimage = wiener2(denoisedimage,[5,5]); % denoising function end disp('image denoised!'); >> image = functiontest('padi.png') Image denoised! >> imshow(image)

20 Matlab Introduction Matrices Plotting Programming Language