MATLAB: Add a Number to a Certain elements and the elements that follows

replace some elements

Hello,
Suppose I have two Matrices A & B
>> A=[1 2 5;7 11 12;15 17 19]
A =
     1     2     5
     7    11    12
    15    17    19
>> B=[2 4 6;10 12 14;16 19 22]
B =
     2     4     6
    10    12    14
    16    19    22
I have a variable say (c) that I will obtain it's value from other commands and used it to find which element in matrix A that equal to it's value.
for example c=2
This means I have to locate the element in Matrix A that =2, which is A(1,2).
Then I want to add a number say (Num=1) to original value of A(1,2) and the elements that follows this elements (i.e. from A(1,3) to A(3,3)), Also I want to add the same number to Matrix B for the elements from B(1,3) to B(3,3), without B(1,2).
How to that?
The Expected Result are:
A =
     1     3     6
     8    12    13
    16    18    20
B =
     2     4     7
    11    13    15
    17    20    23
I am thinking of something like this, but it is totally not correct
A(find(A==c))=Original_Value+Num
B(find(A==c))=Original_Value+Num %Stating from B(1,3) not from B(1,2) as A
Thank you in-advance
Alaa

Best Answer

It's easiest to do this using linear indexing. There is a slight complication in that you want to "index along rows", but linear indexing works down along columns. But, it is still pretty straightforward:
A = [1 2 5;7 11 12;15 17 19];
B = [2 4 6;10 12 14;16 19 22];
c = 2;
Num = 1;
At = A'; % Use the transpose of A, because linear indexing is columnwise.
Bt = B'; % Ditto

idx = find(At==c);
At(idx:end)   = At(idx:end)   + Num;
Bt(idx+1:end) = Bt(idx+1:end) + Num;
A = At'; % Transpose back
B = Bt'; % Ditto
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