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diff function (second derivative)

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jakob ekwall
jakob ekwall 2016-1-25
评论： jakob ekwall 2016-1-25
Say that I have an array A on which I apply the diff function in order to approximate the second derivative. After looking at the results I want to locate the values in A which generated a certain value in ddA. How would one do that?
A =
0.6715
1.2075
0.7172
1.6302
0.4889
1.0347
0.7269
0.3034
0.2939
0.7873
ddA=diff(A,2)
ddA =
-1.0262
1.4032
-2.0543 <--- This value is interesting
1.6871
-0.8536
-0.1156
0.4139
0.5030
How do I find the values in A which generated the interesting value in ddA?

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采纳的回答

Walter Roberson
Walter Roberson 2016-1-25
The N'th value of diff(A,2) is
A(N+2)-2*A(N+1)+A(N)
Note: the value of ddA that you show does not correspond to the value of A that you show.

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