How Can I Efficiently Construct a Specific Matrix in MATLAB?

In summary, the conversation is about constructing a specific matrix for a program in MATLAB. The individual has found one way to do it using in-built functions but is unsure if it is the most efficient way. They are seeking advice from someone familiar with MATLAB and may also ask their teacher for clarification.
  • #1
azdang
84
0
Hi. I'm not sure if anyone here knows MATLAB, but I'm horrible with it. I have to write a program, which I actually figured out how to do, except that I have to first construct a certain matrix. I found one way to do it, but I'm sure it's not how my teacher wants it.

Let A be the nxn matrix with elements aij = -1 for i > j, aii=ain=1, 1<=i<=n, and zero everywhere else.

The only thing I've been successful with is to do this:

B=eye(n,n);B(1:n,n)=1; (This puts 1's on the diagonal and in the last column)

C=tril(-ones(n,n),-1); (This creates a lower triangular matrix with -1's below the diagonal)

Then, A = B+C.

I am sure there must be a more efficient way to construct this matrix that my teacher is expecting, but I'm not sure what it is. Does anyone who has experience with MATLAB know how I might be able to do this? Thank you!
 
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  • #2
You could do it with for loops, but you've recognised some in-built functions of MATLAB and taken advantage of them (correctly!). The best person to ask what is required, of course, is your teacher!
 

Related to How Can I Efficiently Construct a Specific Matrix in MATLAB?

1. How do I create a matrix in MATLAB?

To create a matrix in MATLAB, you can use the matrix function or manually enter the values using square brackets. For example, A = matrix([1 2 3; 4 5 6; 7 8 9]) will create a 3x3 matrix with the given values.

2. How do I perform operations on matrices in MATLAB?

You can use built-in functions such as addition, subtraction, multiplication, and division to perform operations on matrices in MATLAB. You can also use the .* and ./ operators for element-wise operations.

3. How can I access specific elements or rows/columns in a matrix?

To access specific elements in a matrix, you can use indexing. For example, A(1,2) will access the element in the first row and second column of matrix A. You can also use A(1,:) to access the entire first row or A(:,2) to access the entire second column.

4. How do I resize a matrix in MATLAB?

To resize a matrix in MATLAB, you can use the reshape function. For example, A = reshape(A, 6, 2) will reshape matrix A into a 6x2 matrix. You can also use transpose or .' operator to switch the rows and columns of a matrix.

5. Can I save my matrix in MATLAB for future use?

Yes, you can save your matrix in MATLAB using the save function. For example, save('matrixA.mat', 'A') will save matrix A in a file named matrixA.mat for future use. You can also use the load function to load the saved matrix into your workspace.

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