Subscript indices must either be real positive integers or logicals & Index exceeds matrix dimensions.

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ref
ref 2011-10-31
Hello, the code I'm using is shown below. The file I'm trying to read consists of three columns, two important for me (CA and P). CA has random integer values from 0 to 359 and P has totally random values. I'm trying to do some averages for all the values of 0 to 359.
filename='2000rpm_0R.xlsx'
a=xlsread(filename);
CA=a(:,1);
V=a(:,2);
P=a(:,3);
i=0;
j=0;
sum(i)=0;
for i=0:359
for j=2:size(CA)
if CA(j)==i
sum(i)=sum(i)+P(j);
end
end
end
The error I'm getting is that "??? Subscript indices must either be real positive integers or logicals.
Error in ==> Untitled2 at 10 sum(i)=0;". If i erase the term "sum(i)=0" I get another error that "??? Index exceeds matrix dimensions.
Error in ==> Untitled2 at 18 sum(i)=sum(i)+P(j);"
Any ideas how the problems are solved?
  1 个评论
Jan
Jan 2011-10-31
Please use standard code formatting to improve the readability. I've done this for you this time. See "Markup help" on this page.
Do not overwrite the built-in function "sum" by a local variable. This might be working here, but this leads to strange problems frequently.

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采纳的回答

Andrei Bobrov
Andrei Bobrov 2011-10-31
out = [(0:max(CA))',accumarray(CA+1,P,[max(CA)+1,1])]
e.g.
>> CA = randi([0 4],8,1)
CA =
0
0
4
2
2
2
2
1
>> P = randi(12,8,1)
P =
3
11
11
8
5
8
9
11
>> out = [(0:max(CA))',accumarray(CA+1,P,[max(CA)+1,1])]
out =
0 14
1 11
2 30
3 0
4 11
>>
eg averaging
>> out = [(0:max(CA))',accumarray(CA+1,P,[max(CA)+1,1],@mean)]
out =
0 7
1 11
2 7.5
3 0
4 11
>>
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ref
ref 2011-10-31
Your answer worked accumulating all the data, but it does not give me the perspective manipulating them, like averaging, or with an if command deleting error data, and that's why I tried to write code with counters like i and j.

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更多回答（3 个）

Amith Kamath
Amith Kamath 2011-10-31
In MATLAB, unlike in C, the array indices start from 1 and not from 0, and hence all you need to do is to start your loop from 1 instead of 0. The second error is also probably due to this itself, unless the number of elements in P is less than that in C.
ref
ref 2011-10-31
Changing the loop from 0 to 1 seems to fixed the first error, but not the second one. The elements of P are the same in CA.
Amith Kamath
Amith Kamath 2011-10-31
Oh you may also want to initialize sum to sum = zeros(size(P)); just so that MATLAB knows that sum has 359 columns, and as a general note, it's always advisable not to name variables the same as functions, for 'sum' happens to be a function too! Hope this fixes it!

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