computing the cumulative matrix with some conditions

Is there a very concise way to code up computing the cumulative matrix of the following matrix on each column given the following condition that if the element of the column is 1 it adds 0. If it would be 2 it adds 2, if it is 3 it adds to the previous value 4 and if the element of the matrix is 4 it add to the previous value -5

AR =

     1     1     1     1     1     1
     1     1     1     1     1     1
     1     1     2     1     2     1
     1     1     2     1     2     2
     1     1     1     1     1     1
     1     1     1     1     1     1
     2     2     2     2     2     2
     2     2     2     2     2     2
     1     1     1     1     1     1
     1     1     1     1     1     1
     1     2     2     2     2     2
     2     2     2     2     2     2
     1     1     1     1     1     1
     1     1     1     1     1     1
     2     2     2     2     2     2
     2     2     1     2     2     2
     1     1     1     1     1     1
     1     1     1     2     1     1
     2     2     1     2     2     2
     2     2     1     2     2     2
     1     1     1     1     1     1
     1     1     1     1     1     1
     2     1     2     2     2     1
  

Answer 1

[Image Analyst]

Why can't you just make up a look up table like [0, 2, 4, -5] and so on. Then just do a simple for loop for the various conditions such as

1. adding the number from the look up table to the current value, and replacing the current value with it, or
2. adding the number from the look up table to the "previous" element's value

for case #2, I'm not sure whether the result replaces the current element or the previous element.

[Zahra Sheikhbahaee]

I did something like this right now. I was wondering whether there is a better way or not?

indices = find(AR==1);
AR(indices) = 0;
indices = find(AR==4);
AR(indices) =-5;
indices = find(AR==3);
AR(indices) =4;
ac_re = cumsum(AR,1);

[Image Analyst]

That's doing a pure assignment to the number you specify. I thought you wanted to add some numbers together.

Explain exactly, with a sample array, what "it adds to the previous value" means to you.

Also explain what "it adds 2" means to you.

Answer 2

[Matt J]

Is this what you want?

T=[0, 2, 4, -5] ;

result=cumsum(T(AR))