Subtracting 2 cells in an array

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Daniel Lee
Daniel Lee 2020-10-28
评论： Daniel Lee 2020-10-28
Given:
A=[1,3,5,2,6,1];
Is there a function where I can get a difference of first and following cell in above matrix?
For example, output should be = 1-3, 3-5, 5-2,2-6,6-1 = -2,-2,3,-4,5
Finally, is there a way to sum the entire value in the matrix?
Thanks

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Stephen23
Stephen23 2020-10-28
>> -diff(A)
ans =
-2 -2 3 -4 5
>> sum(-diff(A))
ans =
0
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Stephen23
Stephen23 2020-10-28
编辑：Stephen23 2020-10-28
"could you please explain why u put negative sign before diff?"
Because a-b == -(b-a)
In your question you specified that you wanted "...output should be = 1-3...", which is A(1)-A(2). By definition diff returns A(2)-A(1), but simply negating that gives what you asked for: A(1)-A(2) == -(A(2)-A(1))
Another option would be to use indexing and subtraction (but is likely to be less efficient than diff):
>> A = [1,3,5,2,6,1];
>> A(1:end-1)-A(2:end)
ans =
-2 -2 3 -4 5
>> -diff(A)
ans =
-2 -2 3 -4 5

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