Entering Matrices and Vectors in MATLAB
Overview
In this first hands-on introduction to MATLAB you will start to become familiar
with the MATLAB
command window, entering matrices, making assignments, and performing basic
matrix and
vector operations .
Part I
The following commands should be entered and executed to understand how you can
enter
information and obtain results within a MATLAB session. (There is no need to
enter the
comments; they are included for your benefit as you read this document.)
Online help
>> help help |
% Online help can be very useful! |
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• Elementary calculations
>> 2 + 3
>> 4 + sqrt(2)
>> 5 + sqrt(2);
>> ans |
% the semi-colon suppresses the answer
% to see the last answer |
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• Entering Vectors
>> v = [ 1 2 3 ]
>> v2 = [ 1, 2, 3 ]
>> w = [ 1; 2; 3 ]
>> w2 = [ 1
2
3] |
% row vector
% there is no difference between v and v2
% column vector
% is there a difference if we enter
% a column vector as follows? |
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• Entering Matrices
>> A = [ 1 2 3; 4 5 6; 7 8 9 ]
>> A = [ 1, 2, 3; 4, 5, 6; 7, 8, 9 ]
>> A = [ 1, 2, 3; 4, 5, 6; 7, 8, 9 ]
4 5 6
7 8 9] |
% matrix
% the same matrix
% and a third definition
% of the same matrix |
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• Editing Coefficients in a Vector or Matrix
>> w(1) = 0
>> A(2,3)=10 |
% change first entry in vector w
% change one coefficient in matrix A |
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• Transpose
>> w'
>> A' |
% transpose of a column vector
% transpose of a matrix |
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• Accessing Defined Quantities
>> who
>> whos
>> A, v, w
>> |
% list of all assigned variables
% how do who and whos differ?
% type the name of a variable
% to see its contents |
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• Miscellaneous Vector and Matrix Operations
>> B = [ 1 0 -1; 0 3 5; 6 2 3]
>> C = [4 -1 3; 0 2 -5]
>> z = v + 2*w'
>> A + B
>> A - C
>> A * B
>> C * A
>> A * C
>> A'* B'
>> B'* A'
>> (A*B)' |
% define 3x3 matrix B
% define 2x3 matrix C
% compute these quantities
% be sure you understand each result
% (particularly the ones that are not defined)
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% which of A'*B' and B'*A' equals (A*B)'? |
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• Building Matrices from Blocks
>> D = [ A B ]
>> E = [ A B B A ] |
% (or [ A B; B A ]) >> >> |
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• Selecting Sub-Vectors and Sub-Matrices
>> D(:,3)
>> D(2,:)
>> E(1:3,:)
>> E(2:4,1:3) |
% 3rd column of D
% 2nd row of D
% 1st 3 rows of E
% a 3x3 submatrix of E |
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• Special Matrices
>> help eye
>> help zeros
>> help ones |
% identity matrix
% zero matrix
% matrix with all entries equal to one |
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Challenge: Create the 3×6 zero matrix , the 4×4 identity matrix, and the
5×3 matrix
with all entries equal to 2. |
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• Exiting MATLAB
>> quit |
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