EGR 115 Introduction to Computing for Engineers MATLAB Basics 4: Intro to Plotting Wednesday 10 Sept...

EGR 115 Introduction to Computing for Engineers

MATLAB Basics 4: Intro to Plotting

Wednesday 10 Sept 2014 EGR 115 Introduction to Computing for Engineers

http://www.erau.edu/

Lecture Outline


• Intro to Plotting

Slide 2 of 11


MATLAB basicsIntro to Plotting: Plot Function


• Presenting data in graphical form is very useful.• It is quite easy to plot data in MATLAB

The format for the “plot” command is:>> plot(indep_var, dep_var)

o Both the independent variable (say, x) and dependent variable (say, y(x)) should be the same size.

>> x = [0:0.1:3]; % Independent variable>> y = round(x); % Dependent variable>> plot(x, y)

0 0.5 1 1.5 2 2.5 30

0.5

1

1.5

2

2.5

3

Dep VarIndep Var

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• Controlling the style of the line plot Changing the line color (to red)

>> plot(x, y, 'r'); % Choices: c, y, m, k, r, g, b

Change the linestyle to dashed>> plot(x, y, '--'); % Dashed linestyle

Change the line marker to ‘+’>> plot(x, y, '+'); % Marker set to ‘+’

Plot with a magenta colored dotted line and square symbols

0 0.5 1 1.5 2 2.5 30

0.5

1

1.5

2

2.5

3

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• Superimposing Multiple Plots>> z = floor(x);>> plot(x, y, 'm:s', x, z, 'r-');>> title('Multiple Plots')>> xlabel('x')>> ylabel('Magnitude')>> legend('round(x)', 'floor(x)');

• Multiple Plot Windows Precede the plot(..) command with the command “figure”>> figure, plot(…)

o This will create a new figure window!!

0 0.5 1 1.5 2 2.5 30

0.5

1

1.5

2

2.5

3Multiple Plots

x

Mag

nitu

de

round(x)

floor(x)

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MATLAB basicsAdditional Info


• Additional Information: Compute the dot product between two vectors

o Must be the same length (N, say)

o Example: Given, and , then

o Use MATLAB to compute the above dot product.

1

N

i ii

a b a b

1

1* 1 3*0 2*3 5N

i ii

a b a b

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Computing the Norm (i.e., magnitude) of a vectoro Simply the square root of dot product with itself

>> sqrt(dot(v, v)) % or>> norm(v)

What is the norm of ?o Sqrt(1+4+9+16) = Sqrt(30) = 5.4772

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• In Class Problem #1: Given the two vectors and ()

>> v = [4 3 2 2];>> w = [2 5 7 9];

write a script to calculate:

>> c = 2*4 + dot(1./v, w);

>> c = sum(2 + w ./ v);

1

12

N

ii i

c wv

= 18.167

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• In Class Problem #2: Plot both and on the same figure.

o The former line should be blue and dottedo The latter should be red and dash-dottedo Add a legend, axis labels, title, and grid.o Plot limits should be [− , ] for the -axis and [−5, 5] for the 𝜋 𝜋 𝑥

-axis.𝑦– How do we set the axis scaling?– How do we add a grid?– Can we use Greek letters (i.e., )?

Slide 9 of 11

http://www.mathworks.com/help/matlab/ref/text_props.html#String




• In Class Problem #2: Plot both and on the same figure.

-3 -2 -1 0 1 2 3-5

-4

-3

-2

-1

0

1

2

3

4

5A Plot of tan() and d(tan()/dt

(rad)

Mag

nitu

de

tan()

d(tan()/dt

Slide 10 of 11


http://mercury.pr.erau.edu/~bruders/teaching/2014_fall/EGR115/MATLAB_code/

Next Lecture


• MATLAB Applications Vector math

Slide 11 of 11


EGR 115 Introduction to Computing for Engineers MATLAB Basics 4: Intro to Plotting Wednesday 10 Sept...

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