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CIVL 5320

Thomas Ng

MATLAB tutorial

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What is Matlab?

MATrix LABoratory A high-performance language for technical

computingAn easy-to-use interactive environment for

computation, visualization and programming

Getting Started with Matlab

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Interactive: Direct key in command after “>>”>> help>> lookfor CCChang

Off-line: Put all commands into a m-file (name.m) and execute the file as follows>> name (without suffix .m)All commands in the file will be executed

sequentiallyThe m-file has to be in the current directory or

directories set by “pathtool”

Input and Output

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mat-file (name.mat): Contains pre-defined variables, vectors and matrices>> save name

Save all variables into a file called name.mat>> save name CCChang is wonderful

Save variables, vectors or matrices “CCChang”, “is” and “wonderful” into a file called name.mat

>> load nameLoad all variables in the name.mat to the MATLAB

registry

Input and Output

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Do the followings >> help help >> help lookfor >> help plot >> lookfor plot

Put sdof.m and elcen.mat into the current directory >> sdof >> whos >> save temp >> clear all >> whos >> load temp >> whos

Create a m-file that contains the above commands and run the m-file

Exercise

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Sequence of operations >> CCChang

Is CCChang a variable? If not, next Is CCChang a built-in function? If not, next Is CCChang a m-file? If not, next ??? Undefined function or variable 'CCChang‘

Some useful commands Interrupting running the program: Ctrl+c Long command: …

>> x=sin(1)+1+cos(2)+sin(2)+ sin(2)+...

sin(4)+ sin(5)+ sin(6)+ sin(7) Suppress echo: ; Comment: %

Basic Operations

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Some useful commands>> Clear >> Close

Scalar, vector and matrix>> A=123 >> a=321 % >> Rowvector = [12 14 63]>> Colvector= [13; 45; -2]>> Matrix= [1 2 3; 4 5 6; 7 8 9]>> sub_matrix= Matrix( 1:2 , 2:3)

Basic Operations

aA

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Do the followings>> A=123>> A=123 %This is fun!>> A=123; >> x=sin(1)+1+cos(2)+sin(2)+ sin(2)+...

sin(4)+ sin(5)+ sin(6)+ sin(7)>> ColA=[1 ; 2 ; 3]>> RowA=[1 2 3]>> GuessA=[1:10]>> GuessB=[1:3:10]>> GuessC=[1:10]’

Exercise

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>> CC=[1 2 3; 4 5 6; 7 8 9]>> CC=[1:3; 4:6; 7:9]>> subCC1=CC(1:2, 2:3) % what do

you expect?>> subCC2=CC(: , 2:3) % what do

you expect?>> subCC3=CC(1:2, :) % what do you

expect?>> clear all

Exercise

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Basic OperationsPower ^ or .^ a^b or a.^b

Multiplication * or .* a*b or a.*b

Division / or ./ a/b or a./b

or \ or .\ b\a or b.\a

NOTE: 56/8 = 8\56

- (unary) + (unary)

Addition + a + b

Subtraction - a - b

Assignment = a = b (assign b to a)

Element by element operation

Matrix operation

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Special Variables

ans Default variable name for results

pi Value of inf

NaN Not a number e.g. 0/0

i and j i = j =

eps Smallest incremental number

realmin The smallest usable positive real number

realmax The largest usable positive real number

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Command Description

eye Identity matrix

zeros Zeros array

norm Norm of vector or matrix

det Matrix determinant

eig Eigenvalues and eigenvectors

lsim Simulate response of LTI models

for … end Repeat statements (do loop)

demo Run demonstrations

Many many more!Toolboxes contain specialized commands

Built-in Functions

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Do the followings>> RowA=[1 2 3]; ColA=[1 ; 2 ; 3]; >> RowA*ColA>> ColA*RowA>> ColA.*RowA>> ColA.*RowA’>> RowA.*ColA>> RowA.*ColA’>> RowA./ColA>> RowA./ColA’

Exercise

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>> CC=[1 2; 3 4]>> det(CC)>> eye(2)>> zeros(2,2)>> DD=[CC zeros(2,2); zeros(2,2) eye(2)]

Exercise

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Figure control>> figure(x) % Create/go to figure x>> clf(x) % Clear figure x>> close(x)% Close figure x>> title(‘I love MATLAB’) % Figure caption

Plotting>> plot(y) % Plot y versus index>> plot(x,y) % Plot y versus x>> semilogx(x,y) >> semilogy(x,y)>> loglog(x,y) >> plot3(x,y,z)>> subplot(m,n,p) % Create tiled plots

Plotting Figures

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Plotting Figures Plotting control

>> axis([xmin xmax ymin ymax])>> xlabel(‘This is x-axis label’)>> ylabel(‘This is y-axis label’)>> text(x, y, ‘This is a label’) % Add text to

(x,y)

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Open sdof.m file Go through the codes Run sdof.m file Modify the file Re-run

Exercise

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demo