How do I multiply the numbers in a 2D array using a for loop, must be a for loop as part of the course requirements

Hi everyone, this is very basic stuff but I'm new to this. All the steps so far are required by the course.

B=[1:24]

B=reshape(B,6,4)'

A1=B(:,4)

A2=B([2 4],[1 4])

B([3 4],[5 6])=[0 1;1 0]

The next step it to 'create a matrix A3 (using a for/end loop) that has coefficients which are the square of the sine of the corresponding values in matrix B (in degrees), eg. if B(2,3)=20, then A3(2,3)=0.1170',

Now, I'm ok with the sin^2 bit, I managed to get an array with but not using a for loop.

>> sin(B*pi/180).^2

ans =

0.0003 0.0012 0.0027 0.0049 0.0076 0.0109

0.0149 0.0194 0.0245 0.0302 0.0364 0.0432

0.0506 0.0585 0.0670 0.0760 0 0.0003

0.1060 0.1170 0.1284 0.1403 0.0003 0

We need to know how to use the for loop for this for later stage work.

Any help would be greatly appreciated, thank you

Answer 1

[Matt J]

One way:

A3=nan(size(B));

for i=1:size(B,2)
    A3(:,i)=sind(B(:,i)).^2;
end

[Gregory Hind]

Hi, that's perfect, thanks.

Can you explain why for i=1:size(B,2) its B,2 and not just B please?

[Matt J]

size(B,2) gives the number of columns B(:,i).

B=rand(3,5)

B = 3×5

0.3184 0.4519 0.5605 0.1580 0.3940 0.8615 0.8785 0.7961 0.3876 0.0718 0.1113 0.6686 0.2878 0.3678 0.8770

size(B,2)

ans = 5

[Gregory Hind]

Ah ok, thanks again