introduction to matlab
TRANSCRIPT
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Outline:
What is Matlab? Matlab Screen Variables, array, matrix, indexing Operators (Arithmetic, relational, logical ) Display Facilities Flow Control Using of M-File Writing User Defined Functions Conclusion
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What is Matlab? Matlab (MATrix LABoratory) is basically a
high level language which has many specialized toolboxes for making things easier for us
How high?
Assembly
High Level Languages such as
C, Pascal etc.
Matlab
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What are we interested in? Matlab is too broad for our purposes in this
workshop. The features we are going to require is
Matlab
CommandLinem-files
functions
mat-files
Command execution like DOS command
window
Series of Matlab
commands
InputOutput
capability
Data storage/ loading
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Matlab Screen Command Window
type commands
Current Directory View folders and m-files
Workspace View program variables Double click on a variable
to see it in the Array Editor
Command History view past commands save a whole session
using diary
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Matlab editorDebugger
Set/Clear breakingpoint: Sets or clears a break point in the line the cursor is placed.Clear all breakingpoints: Deletes all breaking points.
Step: Executes the current line of the program.
Step in: Executes the current line of the program, if the line calls to a function, steps into the function.
Step out: Returns from a function you stepped in to its calling function without executing the remaining lines individually.Continue: Continues executing code until the next breaking pointQuit debugging: Stops the debugger
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Variables No need for types. i.e.,
All variables are created with double precision unless specified and they are matrices.
After these statements, the variables are 1x1 matrices with double precision
int a;double b;float c;
Example:>>x=5;>>x1=2;
but other formats can be used:>> format long (14 significant figures)>> format short (5 significant figures) >> format short e (exponential notation)>> format long e (exponential notation)>> format rat (rational approximation)
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Array, Matrix
a vector x = [1 2 5 1]
x =1 2 5 1
a matrix xx = [1 2 3; 5 1 4; 3 2 -1]
XX =1 2 35 1 43 2 -1
transpose y = x’ y =1251
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Long Array, Matrix
t =1:10
t =1 2 3 4 5 6 7 8 9 10
k =2:-0.5:-1
k =2 1.5 1 0.5 0 -0.5 -1
B= [1:4; 5:8]
B =1 2 3 45 6 7 8
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Generating Vectors from functions zeros(M,N) MxN matrix of zeros
ones(M,N) MxN matrix of ones
rand(M,N) MxN matrix of uniformly distributed random numbers on (0,1)
x = zeros(1,3)
x =
0 0 0
x = ones(1,3)
x =
1 1 1
x = rand(1,3)
x =
0.9501 0.2311 0.6068
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Matrix Index The matrix indices begin from 1 (not 0 (as in C)) The matrix indices must be positive integer
Given:
A(-2), A(0)
Error: ??? Subscript indices must either be real positive integers or logicals.
A(4,2)Error: ??? Index exceeds matrix dimensions.
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Concatenation of Matrices
x = [1 2], y = [4 5], z=[ 0 0]
A = [ x y]
1 2 4 5
B = [x ; y]
1 2
4 5
C = [x y ;z] Error:??? Error using ==> vertcat CAT arguments dimensions are not consistent.
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Operators (arithmetic)
+ addition- subtraction* multiplication/ division^ power‘ complex conjugate transpose
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Matrices Operations
Given A and B:
Addition Subtraction Product Transpose
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Operators (Element by Element)
.* element-by-element multiplication
./ element-by-element division
.^ element-by-element power
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The use of “.” – “Element” Operation
K= x^2Erorr:??? Error using ==> mpower Matrix must be square.B=x*yErorr:??? Error using ==> mtimes Inner matrix dimensions must agree.
A = [1 2 3; 5 1 4; 3 2 -1]A =
1 2 35 1 43 2 -1
y = A(3 ,:)
y= 3 2 -1
b = x .* y
b=3 4 -3
c = x . / y
c= 0.33 1 -3
d = x .^2
d= 1 4 9
x = A(1,:)
x=1 2 3
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Matlab Functions exp(x), log(x) (base e), log2(x) (base 2), log10(x) (base 10),
sqrt(x)
Trigonometric functions: sin(x), cos(x), tan(x), asin(x), acos(x), atan(x), atan2(x) (entre –pi y pi)
Hyperbolic functions: sinh(x), cosh(x), tanh(x), asinh(x), acosh(x), atanh(x)
Other functions: abs(x) (absolute value), int(x) (integer part ),round(x) (rounds to the closest integer), sign(x) (sign function)
Functions for complex numbers: real(z) (real part), imag(z) (imaginary part), abs(z) (modulus), angle(z) (angle), conj(z) (conjugated)
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Basic Task: Plot the function sin(x) between 0≤x≤4π Create an x-array of 100 samples between 0 and 4π.
Calculate sin(.) of the x-array
Plot the y-array
>>x=linspace(0,4*pi,100);
>>y=sin(x);
>>plot(y)
0 10 20 30 40 50 60 70 80 90 100-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
>>plot(x,y)
0 2 4 6 8 10 12 14-1
-0.5
0
0.5
1
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Plot the function e-x/3sin(x) between 0≤x≤4π Create an x-array of 100 samples between 0 and 4π.
Calculate sin(.) of the x-array
Calculate e-x/3 of the x-array
Multiply the arrays y and y1
>>x=linspace(0,4*pi,100);
>>y=sin(x);
>>y1=exp(-x/3);
>>y2=y*y1;
??? Error using ==> mtimesInner matrix dimensions must agree.
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Plot the function e-x/3sin(x) between 0≤x≤4π Multiply the arrays y and y1 correctly
Plot the y2-array>>y2=y.*y1;
>>plot(y2)
0 10 20 30 40 50 60 70 80 90 100-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
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Display Facilities
plot(.)
stem(.)
Example:>>x=linspace(0,4*pi,100);>>y=sin(x);>>plot(x,y)
Example:>>stem(x,y)
0 2 4 6 8 10 12 14-1
-0.5
0
0.5
1
0 2 4 6 8 10 12 14-1
-0.5
0
0.5
1
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Display Facilities
title(.)
xlabel(.)
ylabel(.)
>>title(‘This is the sinus function’)
>>xlabel(‘x (secs)’)
>>ylabel(‘sin(x)’)0 10 20 30 40 50 60 70 80 90 100
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1This is the sinus function
x (secs)
sin(
x)
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Multiple Graphs
t = 0:pi/100:2*pi;
y1=sin(t);
y2=sin(t+pi/2);
plot(t,y1,t,y2)
grid on
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Multiple Plots
t = 0:pi/100:2*pi;
y1=sin(t);
y2=sin(t+pi/2);
subplot(2,2,1)
plot(t,y1)
subplot(2,2,2)
plot(t,y2)
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Graph Functions (summary) plot linear plot stem discrete plot grid add grid lines xlabel add X-axis label ylabel add Y-axis label title add graph title subplot divide figure window figure create new figure window pause wait for user response
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Operators (relational, logical)
== Equal to ~= Not equal to < Strictly smaller > Strictly greater <= Smaller than or equal to >= Greater than equal to & And operator | Or operator
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Polynomials Polynomials are written in Matlab as a row vector whose dimension
is n+1, n being the degree of the polynomial. Example: x3+2x-7 is written:
>> pol1=
Obtaining the roots: roots (returns a column vector, even though pol1 is a row vector)
>>roots_data=roots(pol1)
A polynomial can be reconstructed from its roots, using the command poly
>> p=poly(roots_data) (returns a row vector)
If the input for poly is a matrix, the output is the characteristic polynomian of the matrix
[ ]1 0 2 -7
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Polynomials
Matlab functions for polynomials
Calculate the value of a polynomial p in a given point x: polyval>>y=polyval(p,x)
Multiplying and dividing polynomials: conv(p,q) y deconv(p,q)
Calculate the derivative polynomial: polyder(p)
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Flow Control
• if statement• switch statement
• for loops• while loops
• continue statement• break statement
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Control Structures
If Statement Syntax
if (Condition_1)Matlab Commands
elseif (Condition_2)Matlab Commands
elseif (Condition_3)Matlab Commands
elseMatlab Commands
end
Some Dummy Examples
if ((a>3) & (b==5))Some Matlab Commands;
end
if (a<3)Some Matlab Commands;
elseif (b~=5) Some Matlab Commands;
end
if (a<3)Some Matlab Commands;
else Some Matlab Commands;
end
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Control Structures
For loop syntax
for i=Index_ArrayMatlab Commands
end
Some Dummy Examples
for i=1:100Some Matlab Commands;
end
for j=1:3:200Some Matlab Commands;
end
for m=13:-0.2:-21Some Matlab Commands;
end
for k=[0.1 0.3 -13 12 7 -9.3]Some Matlab Commands;
end
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Control Structures
While Loop Syntax
while (condition)Matlab Commands
end
Dummy Example
while ((a>3) & (b==5))Some Matlab Commands;
end
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Use of M-FileClick to create a new M-File
• Extension “.m” • A text file containing script or function or program to run
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Use of M-File
If you include “;” at the end of each statement,result will not be shown immediately
Save file as Denem430.m
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Writing User Defined Functions
Functions are m-files which can be executed by specifying some inputs and supply some desired outputs.
The code telling the Matlab that an m-file is actually a function is
You should write this command at the beginning of the m-file and you should save the m-file with a file name same as the function name
function out1=functionname(in1)function out1=functionname(in1,in2,in3)function [out1,out2]=functionname(in1,in2)
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Writing User Defined Functions
Examples Write a function : out=squarer (A, ind)
Which takes the square of the input matrix if the input indicator is equal to 1
And takes the element by element square of the input matrix if the input indicator is equal to 2
Same Name
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Writing User Defined Functions Another function which takes an input array and returns the sum and product
of its elements as outputs
The function sumprod(.) can be called from command window or an m-file as
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Notes: “%” is the neglect sign for Matlab (equaivalent
of “//” in C). Anything after it on the same line is neglected by Matlab compiler.
Sometimes slowing down the execution is done deliberately for observation purposes. You can use the command “pause” for this purpose
pause %wait until any keypause(3) %wait 3 seconds
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Useful Commands
The two commands used most by Matlabusers are
>>help functionname
>>lookfor keyword
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Questions
? ? ? ? ?
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Thank You…