Difference

2 次查看（过去 30 天）
Lizan
Lizan 2011-7-23
I have vector A =
Columns 1 through 5
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
Columns 6 through 10
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
Columns 11 through 15
1.4602 1.4606 1.4609 1.4612 1.4615
0 0 0 0 0
0 0 0 0 0
Columns 16 through 20
1.4619 1.4622 1.4625 1.4629 1.4632
0 0 0 0 0
0 0 0 0 0
Column 21
1.4635
0
0
Why does
diff(A) =
ans =
Columns 1 through 5
0 0 0 0 0
0 0 0 0 0
Columns 6 through 10
0 0 0 0 0
0 0 0 0 0
Columns 11 through 15
-1.4602 -1.4606 -1.4609 -1.4612 -1.4615
0 0 0 0 0
Columns 16 through 20
-1.4619 -1.4622 -1.4625 -1.4629 -1.4632
0 0 0 0 0
Column 21
-1.4635
0
diff(A(1,:)) =
ans =
Columns 1 through 5
0 0 0 0 0
Columns 6 through 10
0 0 0 0 1.4602
Columns 11 through 15
0.0003 0.0003 0.0003 0.0003 0.0003
Columns 16 through 20
0.0003 0.0003 0.0003 0.0003 0.0003
give different result?
  4 个评论
显示 2更早的评论
Andrei Bobrov
Andrei Bobrov 2011-7-23
diff(A,[],1)) % difference row-wise
Daniel Shub
Daniel Shub 2011-7-23
of course it did because you are not reading the documentation of diff. The [] is important. The first argument to diff is the matrix, the second is the order of the difference. You want this to be 1, which is the default so [] works or you could use 1. The third argument is the dimension over which to take the difference. Since you want the difference across rows, you want 2. Grab a pencil and paper and see which one you want.

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采纳的回答

Daniel Shub
Daniel Shub 2011-7-23
If I remember correctly, diff works across the first non-singleton dimension. So diff(A) works across columns and diff(A(1, :)) works across rows.
x = [1,2,3; 4,5,6];
diff(x, [], 1)
ans =
3 3 3
diff(x, [], 2)
ans =
1 1
1 1

更多回答（1 个）

Lizan
Lizan 2011-7-23
I want the difference per row, row one represents one solution and the second row represents another type of solution.
Which of the above will give me the correct solution for my case?

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