Creating a series of random numbers, where the next series is changed by a factor with the previous

For one of my classes, we were assigned a problem where we have to create a series of random numbers that the next series of numbers is the previous multiplied by a factor. We then have to store the numbers in a single matrix.

The code I currently have written keeps appearing with the error code that it is unable to perform the assignment because the left and right sides have a different number of elements. I am looking for advisement on how to change this in order to allow the code to work and fill the matrix.

For this example, I need to create a 5 series, with 25 randon numbers, where the next series is 1/4 of the previous. The numbers produced should be stored in the x single matrix.

The code I started is as follows:

x = zeros(5,25);

count = 1;

for i = 1:5

if i==1

s(count) = randn(1,25);

count = count+1;

elseif i~=1

s(count) = randn(1,25)/4;

count = count +1;

else i == 5

s(count) = count(4,1:25)/4;

end

end

Answer 1

[Paul]

Hi Lily,

The code starts by allocating a 5 x 25 matrix, x. That's good. But then x is never used after that. Assuming that x is supposed to contain the final result, you could proceed as follows.

Pre-allocate the result

x = zeros(5,25);

Assign the first row of the result. Note the use of the double indexing of x. Here, x(1,:) means the "row 1, all columns of x"

x(1,:) = randn(1,25);

Note that a variable or an expression can also be used as an index, e.g., if k = 2, x(k,:) is row 2 and x(k-1,:) is row 1.

Now that the first row if x is filled in we only need to fill in rows 2 -5

for i = 2:5
    % do something here
end

Maybe these hints will allow you to fill in the code in the loop.