bsxfun - @minus - how to divide by maximum

Hello everyone,

I have two arrays:

a = [1; 2; 3]
b = [1; 2; 3; 4]

out = abs(bsxfun(@minus,a,b')./a)

I am getting this:

out = [0    1    2    3
       0.5  0  0.5  1.0
       0.67 0.33 0 0.33]

I am looking for a way to divide not simply by ./a, but to divide by the maximum number in the numerator. So instead of calculating abs(1-3)/1=2 for out(1,3) I would like the calculation to be abs((1-3)/3)=0.67.

Any help is greatly appreciated.

Answer 1

[Bruno Luong]

Do do poor job to explain, up to everyone guess

>> a = [3; 5; 1;]

a =

     3
     5
     1

>> b = [3; 2; 3; 4]

b =

     3
     2
     3
     4


>> abs(a-b')./max(a,b')

ans =

         0    0.3333         0    0.2500
    0.4000    0.6000    0.4000    0.2000
    0.6667    0.5000    0.6667    0.7500

>> abs(bsxfun(@minus,a,b'))./bsxfun(@max,a,b')

ans =

         0    0.3333         0    0.2500
    0.4000    0.6000    0.4000    0.2000
    0.6667    0.5000    0.6667    0.7500

[Ko Fa]

My bad, I just didnt have the apostrophe in max(a,b') after b and was wondering about dimension problems in my original data. Thanks.

Answer 2

[Geoff Hayes]

Ko - if you want to divide by the maximum of a, couldn't you just do

out = abs(bsxfun(@minus,a,b')./max(a))

?

[Ko Fa]

Thanks for your answer, I am actually not just looking to divide by the maximum of a, but to b, if that number happens to be bigger. Your solution works with the example I have provided, so let me try and clarify by another example

a = [3; 5; 1;]
b = [3; 2; 3; 4]

Your Solution gives out this:

out = abs(bsxfun(@minus,a,b')./max(a))
out = [0   0.2 0   0.2
       0.4 0.6 0.4 0.2
       0.4 0.2 0.4 0.6]

What I would want the output to look like is this:

out = [0    0.33 0    0.25
       0.4  0.6  0.4  0.2
       0.67 0.5  0.67 0.75]

An examplary calculation for the upper right term would be: (3-4)/4

I hope this clarifys it, thanks for your time

[Sean de Wolski]

But max of a is 5. So where does the 4 come from??

Also, you don't need bsxfun.

abs((a-b')/max(a))

[Ko Fa]

4 is the maximum numerator, so the number I want to divide with could be from either a or b. whatever the maximum numerator is. hope that helps

Thanks, I'll be taking bsxfun away then.