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Diffstat (limited to 'matlab.html.markdown')
| -rw-r--r-- | matlab.html.markdown | 198 |
1 files changed, 144 insertions, 54 deletions
diff --git a/matlab.html.markdown b/matlab.html.markdown index 3c909153..e72a95ea 100644 --- a/matlab.html.markdown +++ b/matlab.html.markdown @@ -2,9 +2,11 @@ language: Matlab contributors: - ["mendozao", "http://github.com/mendozao"] + - ["jamesscottbrown", "http://jamesscottbrown.com"] + --- -Matlab stands for Matrix Laboratory. It is a powerful numerical computing language commonly used in engineering and mathematics. +MATLAB stands for MATrix LABoratory. It is a powerful numerical computing language commonly used in engineering and mathematics. If you have any feedback please feel free to reach me at [@the_ozzinator](https://twitter.com/the_ozzinator), or @@ -18,13 +20,23 @@ something like this %} +who % Displays all variables in memory +whos % Displays all variables in memory, with their types clear % Erases all your variables from memory +clear('A') % Erases a aprticualr variable +openvar('A') % Open variable in variable editor + clc % Erases the writing on your Command Window -who % Displays all variables in memory -diary % History of session +diary % Toggle writing Command Window text to file ctrl-c % Abort current computation +edit('myfunction.m') % Open function in editor +type('myfunction.m') % Print the source of function to Command Window + +profile viewer % Open profiler + help command % Displays documentation for command in Command Window +doc command % Displays documentation for command in Help Window lookfor command % Searches for a given command @@ -38,6 +50,7 @@ myVariable = 4 % Notice Workspace pane shows newly created variable myVariable = 4; % Semi colon suppresses output to the Command Window 4 + 6 % ans = 10 8 * myVariable % ans = 32 +2 ^ 3 % ans = 8 a = 2; b = 3; c = exp(a)*sin(pi/2) % c = 7.3891 @@ -50,6 +63,12 @@ c = exp(a)*sin(pi/2) % c = 7.3891 3 > 1 || 4 > 1 % OR -> ans = 1 ~1 % NOT -> ans = 0 +% Logicals can be applied to matricies: +A > 5 +% for each element, if condition is true, that element is 1 in returned matrix +A[ A > 5 ] +% returns a vector containing the elements in A for which condition is true + % Strings a = 'MyString' length(a) % ans = 8 @@ -75,7 +94,7 @@ x = [1:10] % x = 1 2 3 4 5 6 7 8 9 10 % Matrices A = [1 2 3; 4 5 6; 7 8 9] -% Rows are seperated with a semi colon, each element is seperated with space or comma +% Rows are separated by a semicolon; elements are separated with space or comma % A = % 1 2 3 @@ -83,6 +102,10 @@ A = [1 2 3; 4 5 6; 7 8 9] % 7 8 9 A(2,3) % ans = 6, A(row, column) +A(6) % ans = 8 +% (implicitly concatenates columns into vector, then indexes into that) + + A(2,3) = 42 % Update row 2 col 3 with 42 % A = @@ -108,77 +131,125 @@ A(1,:) % All columns in row 1 % 1 2 3 -A(:, [3 1 2]) %Rearrange the columns of original matrix +[A ; A] % Concatenation of matrices (vertically) +%ans = + +% 1 2 3 +% 4 5 42 +% 7 8 9 +% 1 2 3 +% 4 5 42 +% 7 8 9 + +[A , A] % Concatenation of matrices (horizontally) + +%ans = + +% 1 2 3 1 2 3 +% 4 5 42 4 5 42 +% 7 8 9 7 8 9 + + + +A(:, [3 1 2]) % Rearrange the columns of original matrix %ans = % 3 1 2 % 42 4 5 % 9 7 8 -A(1, :) =[] %Delete the first row of the matrix - size(A) % ans = 3 3 -A' % Transpose the matrix +A(1, :) =[] % Delete the first row of the matrix -[A ; A] % Concatenation of matrices -%ans = +A' % Hermitian transpose the matrix +% (the transpose, followed by taking complex conjugate of each element) +transpose(A) % Transpose the matrix, without taking complex conjugate -% 1 2 3 -% 4 5 42 -% 7 8 9 -% 1 2 3 -% 4 5 42 -% 7 8 9 -%Element by Element Arithmetic VS Matrix Arithmetic +% Element by Element Arithmetic vs. Matrix Arithmetic A * B % Matrix multiplication A .* B % Multiple each element in A by its corresponding element in B -%Plotting -x = 0:.10:2*pi % Creates a vector that starts at 0 and ends at 2*pi with increments of .1 -y = sin(x) +% Plotting +x = 0:.10:2*pi; % Creates a vector that starts at 0 and ends at 2*pi with increments of .1 +y = sin(x); plot(x,y) xlabel('x axis') ylabel('y axis') title('Plot of y = sin(x)') axis([0 2*pi -1 1]) % x range from 0 to 2*pi, y range from -1 to 1 -plot(x,y1,’-’,x,y2,’--’,x,y3,’:’) % For multiple functions on one plot +plot(x,y1,'-',x,y2,'--',x,y3,':'') % For multiple functions on one plot +grid on % Show grid; turn off with 'grid off' + +axis square % Makes the current axes region square +axis equal % Set aspect ratio so data units are the same in every direction + +scatter(x, y); % Scatter-plot +hist(x); % Histogram +z = sin(x); +plot3(x,y,z); % 3D line plot -% .mat files -% Save the variables in your Workspace +pcolor(A) % Heat-map of matrix: plot as grid of rectangles, coloured by value +contour(A) % Contour plot of matrix +mesh(A) % Plot as a mesh surface -%M-file Scripts -%A script file is an external file that contains a sequence of statements. -%Better than typing your code in the Command Window -%Have .m extensions +h = figure %C reate new figure object, with handle f +figure(h) %M akes the figure corresponding to handle h the current figure +% Properties can be set and changed through a figure handle +h = plot(x, y); +set(h, 'Color', 'r') +% 'y' yellow; 'm' magenta, 'c' cyan, 'r' red, 'g' green, 'b' blue, 'w' white, 'k' black +set(h, 'LineStyle', '--') + % '--' is solid line, '---' dashed, ':' dotted, '-.' dash-dot, 'none' is no line +get(h, 'LineStyle') -%M-file Functions -%Programs that accept inputs and return an output -%Have .m extensions -% double_input.m - naming your ,m file the same as you call it in the file is required + +% Variables can be saved to .mat files +save('myFileName.mat') % Save the variables in your Workspace +load('myFileName.mat') % Load saved variables into Workspace + + +% M-file Scripts +% A script file is an external file that contains a sequence of statements. +% They let you avoid repeatedly typing the same code in the Command Window +% Have .m extensions + + +% M-file Functions +% Like scripts, and have the same .m extension +% But can accept input arguments and return an output +% Also, they have their own workspace (ie. different variable scope) +% double_input.m - .m file name must be same as function name in file function output = double_input(x) %double_input(x) returns twice the value of x output = 2*x; end double_input(6) % ans = 12 -%User input + +% You can also have subfunctions and nested functions. +% Subfunctions are in the same file as the primary function, and can only be +% called from within that function. Nested functions are defined within another +% functions, and have access to both its workspace and their own workspace. + + +% User input a = input('Enter the value: ') -%Reading in data +% Reading in data fopen(filename) -%Output +% Output disp(a) % Print out the value of variable a disp('Hello World') % Print out a string -fprintf % More control display to Command Window +fprintf % Print to Command Window with more control -%Conditional statements +% Conditional statements if a > 15 disp('Greater than 15') elseif a == 23 @@ -187,7 +258,9 @@ else disp('neither condition met') end -%Looping +% Looping +% NB. looping over elements of a vector/matrix is slow! +% Where possible, use functions that act on whole vector/matrix at once for k = 1:5 disp(k) end @@ -197,8 +270,13 @@ while (k < 5) k = k + 1; end +% Timing code execution: 'toc' prints the time since 'tic' was called +tic +A = rand(1000); +A*A*A*A*A*A*A; +toc -%Connecting to a MySQL Database +% Connecting to a MySQL Database dbname = 'database_name'; username = 'root'; password = 'root'; @@ -206,7 +284,7 @@ driver = 'com.mysql.jdbc.Driver'; dburl = ['jdbc:mysql://localhost:8889/' dbname]; javaclasspath('mysql-connector-java-5.1.xx-bin.jar'); %xx depends on version, download available at http://dev.mysql.com/downloads/connector/j/ conn = database(dbname, username, password, driver, dburl); -sql = ['SELECT * from table_name where id = 22'] %Example sql statement +sql = ['SELECT * from table_name where id = 22'] % Example sql statement a = fetch(conn, sql) %a will contain your data @@ -228,14 +306,19 @@ ceil(x) floor(x) round(x) rem(x) -rand -randi +rand % Uniformly distributed pseudorandom numbers +randi % Uniformly distributed pseudorandom integers +randn % Normally distributed pseudorandom numbers % Common constants pi NaN inf +% Solving matrix equations (if no solution, returns a least squares solution) +x=A\b % Solves Ax=b +x=B/a % Solves xa=B + % Common matrix functions zeros(m,n) % m x n matrix of 0's ones(m,n) % m x n matrix of 1's @@ -243,30 +326,37 @@ diag(A) % Extracts the diagonal elements of a matrix eye(m,n) % Indentity matrix inv(A) % Inverse of matrix A det(A) % Determinant of A -eig(A) %Eigenvalues and eigenvectors of A +eig(A) % Eigenvalues and eigenvectors of A +trace(A) % Trace of matrix - equivalent to sum(diag(A)) isempty(A) % Tests if array is empty +all(A) % Tests if all elements are nonzero or true +any(A) % Tests if any elements are nonzero or true isequal(A, B) %Tests equality of two arrays -numel(A) %Number of elements in matrix +numel(A) % Number of elements in matrix triu(x) % Returns the upper triangular part of x tril(x) % Returns the lower triangular part of x cross(A,B) % Returns the cross product of the vectors A and B -dot(A,B) % Returns the scalar product of the vectors A and B. A and B must be vectors of the same length. +dot(A,B) % Returns scalar product of two vectors (must have the same length) transpose(A) % Returns the transpose of A +flipl(A) % Flip matrix left to right % Common vector functions -max %largest component -min %smallest component -length %length of a vector -sort %sort in ascending order -sum %sum of elements -prod %product of elements -median %median value -mean %mean value -std %standard deviation - +max % largest component +min % smallest component +length % length of a vector +sort % sort in ascending order +sum % sum of elements +prod % product of elements +mode % modal value +median % median value +mean % mean value +std % standard deviation +perms(x) % list all permutations of elements of x ``` ## More on Matlab * The official website [http://http://www.mathworks.com/products/matlab/](http://www.mathworks.com/products/matlab/) +* The official MATLAB Answers forum: [http://www.mathworks.com/matlabcentral/answers/](http://www.mathworks.com/matlabcentral/answers/) + |