comparing and addition of two matrices

a=[9,41,48,0,0,0,0,0;15,47,56,0,0,0,0,0;25,67,0,0,0,0,0,0];b=[21;11;30]; I am having three rows in a and b. I need to compare a with b for example i am taking 21 from b and comparing with the first row of a, first row first column value is 9, but b value is 21 its greater than a so the remaining columns in first row should be added by 5 except zero [9, 46, 53,0,0,0,0,0]. Similarly in the second row of a has to be compared with second row of b [20,52,61,0,0,0,0,0]. Third row [25,72,0,0,0,0,0,0]. Finally my a=[9,46,53,0,0,0,0,0;20,52,61,0,0,0,0,0;25,72,0,0,0,0,0,0]. suggest with some points.

[José-Luis]

How to ask a question

[Geoff Hayes]

I think if you just write out the pseudo code for this problem, then it would be easy for you to replace that with code

for each row in a do
   if first element of row is less than equivalent row element of b do
     find all elements of this row from second index to end that aren't
     zero and add five
   end
end

The loop and the if are easy (if stuck, type help size to see how size can be used to determine the number of rows in a) and then to find all elements that aren't zero, type help find for hints.

[dpb]

That isn't quite the rule he gave, though--he adds for all columns from 2:end irrespective of the first column comparison; it's only that first column that is dependent on the value in b, apparently. (At least that's what his example gives as a result.)

[Geoff Hayes]

Huh. I could have sworn the second row of b didn't have 5 added to the elements from 2:end. I see now how it does from 1:end though...

Answer 1

[dpb]

Look up "logical addressing"...

>> ix=[b<a(:,1) a(:,2:end)>0];
>> a(ix)=a(ix)+5
a =
   9    46    53     0     0     0     0     0
  20    52    61     0     0     0     0     0
  25    72     0     0     0     0     0     0

[Bathrinath]

Thank you sir. I bow you for your logical thinking.

[dpb]

Chuckles...thanks, glad I did seemingly get the intent correct; wasn't really sure if the actual example really was what was intended or not.