I read MATLAB diff.m readme, still couldn't figure out the following:

    a = [1 2 3]'
    b = [3 2 1 4; 1 1 1 5; 5 5 5 6]
    diff([a b]') = 
    2  -1  2
   -1   0  0
   -1   0  0
    3   4  1

what rule is MATLAB applying here? does MATLAB apply different rule if one of the matrices (i.e. a or b) is logical matrix? or both a and b are logical matrix?

CodePudding user response：

a = 
[1
 2
 3]

So,

[a b] = 
[ 1 3 2 1 4
  2 1 1 1 5
  3 5 5 5 6 ]

and thus

[a b]' = 
[ 1 2 3
  3 1 5
  2 1 5
  1 1 5
  4 5 6 ]

and then diff takes the differences along the first dimension whose size is not 0 (i.e. down each column). This gives the result

diff([a b]') = 
[ 2 -1  2
 -1  0  0
 -1  0  0
  3  4  1 ].

CodePudding user response：

MATLAB applies the same rule regardless of the input matrices. Run your code line-by-line in the command window and see.

a and b are like this:

>> a = [1 2 3]'
a =
     1
     2
     3
>> b = [3 2 1 4; 1 1 1 5; 5 5 5 6]
b =
     3     2     1     4
     1     1     1     5
     5     5     5     6

then [a b]':

>> [a b]'
ans =
     1     2     3
     3     1     5
     2     1     5
     1     1     5
     4     5     6

Now apply the diff rule on this as follows:

[ row 2 - row 1 ]
[ row 3 - row 2 ]
[ row 4 - row 3 ]
[ row 5 - row 4 ]

you will get

>> diff([a b]')
ans =
     2    -1     2
    -1     0     0
    -1     0     0
     3     4     1