Expanding a matrix with for loop

A product from a for loop is a 1 x 20 matrix alfa and 1 x 20 matrix m.

I would like to expand the matrix alfa to 40 x 20 matrix by adding an equidistant increment with linspace to every value in the row.

I tried the following:

for j=1:numel(alfa)

b(j)= linspace(alfa(j),2*alfa(j),40)

r0(b)=m(b)./(cosd(alfa(b)/2));

end

but it's not working and I can't think of a solution.

Please let me know if you have a suggestion.

Answer 1

[Dev]

Hi Mareeah,

To expand the matrix ‘alfa’ from 1x20 to 40x20, we can first declare the expanded matrix. Next, we can use the “linspace” function to make sure each column is a linspace from alfa(j) to 2*alfa(j) (40 points, as referred in the code provided above). I have attached a reference code snippet below which achieves the same-

% Expand alfa 
alfa_expanded = zeros(40, 20); 
for j = 1:20 
    alfa_expanded(:,j) = linspace(alfa(j), 2*alfa(j), 40).'; 
end 

For more information regarding the usage of the “linspace” function in MATLAB, please refer to the documentation link below-

https://www.mathworks.com/help/releases/r2024b/matlab/ref/double.linspace.html

Finally, since the code provided above calculates ‘r0’ for each value, we can do the same on the expanded matrix outside the ‘for’ loop, as shown below-

% Compute r0 
r0 = m ./ cosd(alfa_expanded/2); 

I hope the above approach helps resolves your query.