Dividing an entire row by every element of a column

Hi,

I have a 20x 60 matrix. I am trying to divide an entire row (3rd) by every element of the first column.

I know it should be solved using for loop but I am still fairly new to MATLAB, so I don't know the syntax of For Loop. Would appreciate any help.

[Torsten]

Could you give an example with a 3x6 matrix of what exactly you mean ?

[the cyclist]

The third row has 60 elements. The first column has 20 elements. So, it is very unclear what it means to do this division.

Also, it's not clear whether you are trying make changes to the original matrix, or create a matrix.

[Nany]

my_matrix= [ 2 4 8 10 10 8; 6 16 16 20 18 30]
second_row= my_matrix(2, :)
first_column= my_matrix (:,1)

I want to divide every element in the second row by every element in the first colmun (2 and 6 in this case)

Is it possible in matlab?

[Torsten]

What we'd like to know is: what would be the result for your test matrix from above ?

Answer 1

[Voss]

Like this? (Using a 5x3 matrix as an example.)

A = (1:5).'+3*(0:2)

A = 5×3

1 4 7 2 5 8 3 6 9 4 7 10 5 8 11

A(3,:)./A(:,1) % 3rd row divided by first column

ans = 5×3

3.0000 6.0000 9.0000 1.5000 3.0000 4.5000 1.0000 2.0000 3.0000 0.7500 1.5000 2.2500 0.6000 1.2000 1.8000

%   3/1     6/1     9/1
%   3/2     6/2     9/2
%   3/3     6/3     9/3
%   3/4     6/4     9/4
%   3/5     6/5     9/5

[Nany]

Thank you!

Let's say I want to multiply every element in the second column of the original matrix by 7. Can I use the operator ".*" ?

As in

C= A(:, 2) .* 7

[Voss]

You're welcome!

Yes, that will work. You could also use "*" (without the period) since 7 is a scalar, not a vector.