Trapz abnormal behavior. Error:Subscript indices must either be real positive integers or logicals.

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Giorgos Papakonstantinou
When I enter:
>> trapz(2,2)
ans =
0
When I enter:
>> trapz(2.2,2.2)
Subscript indices must either be real positive integers
or logicals.
Error in ipermute (line 23)
inverseorder(order) = 1:numel(order); % Inverse
permutation order
Error in trapz (line 73)
if ~isempty(perm), z = ipermute(z,perm); end
Why trapz is having trouble in such case?

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回答（2 个）

Azzi Abdelmalek
Azzi Abdelmalek 2013-8-24
What are you expecting with trapz(2.2,2.2)? to compute the integral along x, you will need at least 2 points
  2 个评论
Giorgos Papakonstantinou
Giorgos Papakonstantinou 2013-8-24
trapz(2,2) which yields 0 is two points?. The numerical integral should be zero. So I expect 0. If that was the case then it should fail also at trapz(2,2).
Azzi Abdelmalek
Azzi Abdelmalek 2013-8-24
%(2,2) is one point with x=2 and y=2.
% tarpz(2,2) returns 0, but I'm not sure if it's computing an integral, even the expected result is 0.

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Walter Roberson
Walter Roberson 2013-8-24
When you use trapz() and the second argument is a scalar, then you are invoking the behavior trapz(Y,DIM) where DIM is to be a dimension number, which must be a positive integer.

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