MATLAB: Comparing relevant elemnts of two matrix

matrix

Hi all,
I have two matrics like below:
      a=[9 7 NaN; 6 3  8; 15 NaN 5; NaN 4 2];
      b= [10,14,NaN;10,10,13;10,NaN,10;NaN,10,10;] ;
I want to see if each element of "a" is less than or equal to its corresponding element in "b"?
 how can I write this program .
 Thanks in advance.

Best Answer

Maybe this is what you want:
a=[9 7 NaN; 6 3  8; 15 NaN 5; NaN 4 2]
b= [10,14,NaN;10,10,13;10,NaN,10;NaN,10,10;]
% Subtract the two. 
% The value will be negative when a(r,c) < b(r,c).
differenceMatrix = a-b
% Make that into a boolean map of where a<b.
% It will be true (1) where a<b.
mapOfWhereAisSmallerThanB = differenceMatrix<0
% Just for fun, do the converse.
% Make that into a boolean map of where b<a.
% It will be true (1) where b<a.
mapOfWhereBisSmallerThanA = differenceMatrix > 0
% See if all non-Nan values have a<b
nonNanIndexes = ~isnan(a) & ~isnan(b)
if all(differenceMatrix(nonNanIndexes) < 0)
  msgbox('All of a < b');
else
  msgbox('Not all of a is < b');
end
In the command window:
a =
     9     7   NaN
     6     3     8
    15   NaN     5
   NaN     4     2
b =
    10    14   NaN
    10    10    13
    10   NaN    10
   NaN    10    10
differenceMatrix =
    -1    -7   NaN
    -4    -7    -5
     5   NaN    -5
   NaN    -6    -8
mapOfWhereAisSmallerThanB =
     1     1     0
     1     1     1
     0     0     1
     0     1     1
mapOfWhereBisSmallerThanA =
     0     0     0
     0     0     0
     1     0     0
     0     0     0
nonNanIndexes =
     1     1     0
     1     1     1
     1     0     1
     0     1     1
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