Why use MATLAB? Mathematcal computations. Used a lot for problem solving. Statistical Analysis (e.g., mean, min) Visualisation (1D-3D)

Transcription

1 MATLAB(motivation) Why use MATLAB? Mathematcal computations Used a lot for problem solving Statistical Analysis (e.g., mean, min) Visualisation (1D-3D) Signal processing (Fourier transform, etc.) Image processing (e.g., animations) Pattern recognition

2 2. Lithosphere integrity and growth P velocity isosurface (-1% and +1%)

3 Starting Matlab Free Access: Where to download among the products, find mathematics Find the appropriate version and download using student CCID. When installing, only one of the installing options (e.g., not using a license) works. I also suggest that all the items are installed (by default only a few are selected among many different packages).

4 Starting Matlab Double click on the Matlab icon, or on unix systems type matlab at the command line. After startup Matlab displays a command window that is used to enter commands and display results. Enter Commands at the command prompt: >> 3+4 for full version version Matlab responds to commands by printing text in the command window, or by opening a figure window for graphical output. Toggle between windows by clicking on them with the mouse.

5 Matlab screen of R2018b Launch Pad/Workspace: Used to browse documentation, or view values of variables in the workspace File browser For the current folder Command window: where your commands are input and excuted. Details window: shows the detail of the files you select under the Current Folder above. A key purpose is to see the first line of a M-file (which is why you should have comments). Command History window: keeps tracks of earlier commands (why? Ex: allows you to put them into a script file if you want later, or reexecute some or a block of them).

6 Simple usages (e.g., Calculator) Enter formula at the command prompt >> 10+2*3 >> (105-32)*5/9 ans = 16 ans = (yes, med time!) mathematical symbols: Add: + subtract: - Multiply: * Divide: / Exponent: ^ Built-in functions (provided by MATLAB) sin() cosh() log log10. sqrt() exp()

7 Getting help Many ways to get help help sin log Natural logarithm. log(x) is the natural logarithm of the elements of X. Complex results are produced if X is not positive. See also log1p, log2, log10, exp, logm, reallog. Reference page for log Other functions named log lookfor sin Find all functions that contain sin which Tells you where function sin() is defined edit log10 Provides details of log10 above the command window Press the fx icon to the left of >> Function browser by categories

8 Define variables User defined variables (case sensitive) >> a =3; Workspace Prevents printouts >> a = 10; % Overwritten >> b = sin(a); %. Both are doubles without type cast!

9 Define variables Built-in variables e.g. pi i j What about Intrinsically, variables in MATLAB are vectors and matrices! Every variable is an array! i = 3+5i, or i=5+6j? Or a= 3+5i; b=3; a+b? a+b*i? By defining a=10, we are essentially defining an array a with 1 element, which turns out to have a value of 10 (integer type) Scalar: array with 1 element Vector: an array with 1 dimension ---à a sequence of elements, i.e., a matrix with 1 row or 1 column Row vector >> a = [1, 2, 3] >> a = [1 2 3] column vector >> a = [1; 2; 3]

10 Saving your work As scripts (M-files, with.m extension such as mytest.m), can be done with GUI or by highlighting commands from command history window using the right mouse click. Remove clutter on the screen by >> clc % does not affect Workspace and variables Or >>clear %actually removes everything from Workspace and all variable definitions and answers As function scripts (M-files, more self contained and variables inside functions, which are not visible to the other codes or workspace unless defined as global). Use GUI by clicking on the right triangular icon and save or save( mytest.mat ) with options like save( mytest.mat, a ) MAT files (saved workspace and all the global variables only, including arrays and answers) Up arrow cycles through your earlier commands Executing by loading via MATLAB GUI

11 The working directory is controlled by >> dir >> cd catalogue >> pwd The path variable defines where matlab searches for m-files >> path >> addpath >> pathtool >> which function

12 Flow control - selection Syntax: if <logical expression> <commands> elseif <logical expression> <commands> else <commands> end Example: height =185; if height > 180 disp( tall, for me anyway ) elseif height<150 disp( small ) else disp( average ) end

13 Logical expressions Relational operators == (equal to) ~= (not equal) < (less than) <= (less than or equal to) > (greater than) >= (greater than or equal to) Logical operators & (and) (or) ~ (not) Logical functions xor isempty any all Example: X=20; if (x>=0) & (x<=10) disp( x is in range from 0 to 10 ) else disp( x is greater than 10 ) end x is greater than 10