Subtracting elements in an array

hi there,

I have an array lets say

 A=[10 9 10; 1 2 3; 4 5 6]

How can create an array like this?

 B=[10-1 9-2 10-3;10-1-4 9-2-5 10-3-6]

thanks in advance!

Nikolas

Answer 1

[Star Strider]

If I understand correctly what you are asking, this will work:

A=[10 9 10; 1 2 3; 4 5 6]
B = cumsum(-A(2:end,:))+A(1,:)

A =
    10     9    10
     1     2     3
     4     5     6

B =
     9     7     7
     5     2     1

[Walter Roberson]

Alternately

A(1,:) - cumsum(A(2:end,:))

My first mental version was indeed in terms of negating and then cumsum, but then I realized that wasn't necessary.

[Nikolas Spiliopoulos]

Yeah that's exactly what i mean thanks a lot!!

[Star Strider]

Our pleasure!

[Nikolas Spiliopoulos]

hi again, I tried it but I get an error "matrix dimensions must agree"! any ideas how to fix it? thanks

[Star Strider]

Please post your matrix and code. That error should not occur with the sort of matrix you originally posted.

[Nikolas Spiliopoulos]

>> A=[10 9 10; 1 2 3; 4 5 6] B = cumsum(-A(2:end,:))+A(1,:)

A =

    10     9    10
     1     2     3
     4     5     6

Error using "+ " Matrix dimensions must agree.

[Star Strider]

The most recent versions of MATLAB do this minimal expansion automatically. Somewhat less recent versions require the bsxfun function to do the same operation.

This should work for you:

B = bsxfun(@minus, A(1,:), cumsum(A(2:end,:)));

(I tested it, and it gives the same result as our eariler code versions.)

[Nikolas Spiliopoulos]

ok got it, it works! thanks again mate..!!!

[Star Strider]

Our pleasure!