trouble using "mean" function in MATLAB?

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Anand Anand
Anand Anand 2012-10-23
consider A=[1 2 3] if i use mean(A(1):A(3)) it gives 2 which is the mean of first element and third element of A.
if A=[3 2 1],and if i use mean(A(1):A(3)) then it says NaN. Why should this occur?shouldnt the command just give the mean of the first and third digit in the array?Any help will be appreciated...

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回答（2 个）

Azzi Abdelmalek
Azzi Abdelmalek 2012-10-23
Maybe you want
mean(A(1:3))
Matt Fig
Matt Fig 2012-10-23
You are creating a vector with the elements of A, rather than indexing into A with a vector. Look at what happens:
A = [1 2 3];
B = A(1):A(3) % Same as:
B2 = 1:3 % Read: make a vector from 1 to 3 in steps of 1
isequal(B,B2)
A = [3 2 1];
B = A(1):A(3) % Same as:
B2 = 3:1 % Read: make a vector from 3 to 1 in steps of 1
isequal(B,B2)
Probably what you want to do is index into A with a vector:
A(1:3) % Read: take elements 1 through 3 of A.

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