I am trying to get a 3*3 diagnol matrix by using the following code. But the resultant matrix dimensions exceed 3*3 matrix.

theta = 0:pi:2*pi;
a = cos(theta)+sin(theta);
A = ismatrix([[a,0,0],[0,a,0],[0,0,a]]);
a = cos(theta)+sin(theta);
A = ismatrix([[a,0,0],[0,a,0],[0,0,a]]);
B = [a 0 0;0 a 0;0 0 a];

[Stephen23]

@Ameer Hamza: what do you expect

[[a,0,0],[0,a,0],[0,0,a]]

to do? Commas always indicate concatenation along the second dimension, so your code will simply produce one row vector. Your code is simply equivalent to this:

[a,0,0,0,a,0,0,0,a]

How to create vectors and matrices by concatenating elements together is explained in the introductory tutorials (which are highly recommended for all beginners):

https://www.mathworks.com/help/matlab/getting-started-with-matlab.html

[Ameer Hamza]

Thanks for the response, what i want to do is to get set of numbers in the matrix while keeping size of the matrix same. for example: a = 0:2*pi b = cos(a)+sin(a) c = [b 0 0;0 b 0;0 0 b] I can use diag to get the response keeping the matrix dimension same but it only gives me the final values. for theta = 0:2*pi a = cos(theta)+sin(theta); c = [a 0 0;0 a 0;0 0 a] end doing so gives me the result but i get number of matrices with each values of theta but the workspace stores just the final matrix.

[Stephen23]

@Ameer Hamza: The point of my comment is that your code does not create a matrix.

Answer 1

[Ameer Hamza]

If you want the element of a to be the diagonal of B, you need something like this

theta = 0:pi:2*pi; 
a = cos(theta)+sin(theta); 
B = diag(a);

[Ameer Hamza]

Thanks but if the matrix elements are not diagonal it then results in either matrix with high dimensions or matrix with just the final values of theta.

[Ameer Hamza]

Can you show an example output matrix you want?

theta = 0:pi:2*pi;
a = cos(theta)+sin(theta);
a =
   [1 -1 1]

how do you want elements of a in your 3x3 matrix

[Ameer Hamza]

Thank you. My problem is that Matlab dont store all the values of matrix a , it store only the final value. I tried the method in this video https://blogs.mathworks.com/videos/2007/08/20/matlab-basics-video/ but it increase the dimension of the matrix. I need only (3*3) matrix.

[Ameer Hamza]

In that video, for loop is used. In my code there is not for loop and MATLAB does store all the values of a. Have you tried running the code? The following code gives a vector (containing all values of a)

theta = 0:pi:2*pi;
a = cos(theta)+sin(theta);
disp(theta);
 ans = 
   0    3.1416    6.2832
disp(a);
 ans = 
   1 -1 1

You still did not explain, what do you want in MATRIX?