Matlab Review Picker Engineering Program Smith College EGR 301 - - PDF document

Matlab Review

Picker Engineering Program Smith College EGR 301

January 25, 2005 Judith Cardell

• Basic commands
• Running script files and capturing output
• Matrix manipulations
• Plotting

Matlab Hints

• Matlab is available on the EGR, and

most other, computers on campus

• Icon:

MATLAB 6.5.lnk

Matlab Commands

• pwd
• ls
• cd
• edit
• help command
• See also webpage links and Appendix E
• f the EGR 220 text

Matlab Hints

Matlab Script File

• Create a ‘.m’ file in the editor

– Type “ edit filename ” in Matlab

• Include comments!!

– Header

• Filename
• Assignment and brief description
• Your name and date

– Comments throughout

• ‘%’ is used to indicate a comment line
• The semicolon tells Matlab not to echo the

information on the given line to the screen Node-voltage equations by inspection

• Find i1, i2, i3 and i (problem 3.41)

Analysis by Inspection

Ohm’s law V = IR RI = V

– Rkk = sum of R in mesh k – Rjk = negative sum of R in common between meshes j and k

% % MatlabSample1.m % Your name, date ... % % Problem number 3.41

R = [ 12 -2 0

• 2 7 -1

0 -1 6]; % The ; tells Matlab ... V = [6 -8 2]'; % Note the '

% % Our equation is R I = V % Solve for I by solving I = inverse(R) V %

I = inv(R)*V % There is no ; here i = I(3) - I(2)

Running MatlabSample1.m

• Run your script (.m) file in Matlab

–Once it does what you want, record your results

• To record your results, type

diary filename.txt name-of-.m-file (note, the output will scroll across the screen when you run your script. The name-of- .m-file in this example is MatlabSample1) diary off

>> diary Sample1Out.txt >> MatlabSample1 I = 0.3291

• 1.0256

0.1624 i = 1.1880 >> diary off

Problem 3.41, output from MatlabSample1.m I = % Current vector, i1, i2 and i3 0.3291

• 1.0256

0.1624 i = % Current through 1Ω resistor 1.1880

EDIT Your Diary File!!!! General Matrix Manipulations

• Matrix

– An m x n collection of data – (rows x columns)

• Vector

– An m x 1 array, or – A 1 x n array

• Matrix manipulation in Matlab

– The ‘:’ operator to select rows, columns or subsets of rows and columns

>> A = [ 1 2 3 4 ; 5 6 7 8 ; 3 4 5 6 ; 2 6 4 5] A = 1 2 3 4 5 6 7 8 3 4 5 6 2 6 4 5 >> B = [A(1,:)] B = 1 2 3 4 >> C = [A(:,2)] C = 2 6 4 6 >> D = [A(1:2,2)] D = 2 6 >> A = [ 1 2 3 4 ; 5 6 7 8 ; 3 4 5 6 ; 2 6 4 5] A = 1 2 3 4 5 6 7 8 3 4 5 6 2 6 4 5 >> F = [A(1,:) A(3,:)] F = 1 2 3 4 3 4 5 6 >> G = [A(1,:) ; A(3,:)] G = 1 2 3 4 3 4 5 6

Matrix Multiplication

• Standard matrix multiplication

– A * B

• Element-wise multiplication

– Do Not mistake this for matrix multiplication – A .* B

>> A = [ 1 1 ; 1 1; 1 1] A = 1 1 1 1 1 1 >> B = A‘ ( Matrix transpose ) B = 1 1 1 1 1 1 >> C = B * A C = 3 3 3 3 >> D = B .* A ??? Error using ==> .* Matrix dimensions must agree. >> D = B(:,1:2) .* A(1:2,:) D = 1 1 1 1

Plotting

• 2-D plots

– Input or create x- and y- axis data sets – plot (x, y, ‘b--’) – Also contour(), based on x, y, z data

• 3-D plots

– Input or create x-, y- and z- axis data sets – mesh (x, y, z) – Or, setup x- and y-axes with meshgrid() – Also:

surf()

Plotting

• Scale axes with axis() command
• To create time step data for x-axis

t = [start-value: step-size: end-value]

>> t = [0:0.5:5] t = 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

• Label axes and plots

– title(), xlabel(), ylabel()

• For plotting more than one line ‘hold on’

and ‘hold off’ can be useful