x.abs()?

조회 수: 18 (최근 30일)
Shunchao Wu
Shunchao Wu 2011년 11월 11일
>> x=-1;
>> x.abs()
??? Attempt to reference field of non-structure array.
Why?
Notice that Matlab Help says "All MATLAB data types are implemented as object-oriented classes."

채택된 답변

Fangjun Jiang
Fangjun Jiang 2011년 11월 11일
That is true, but it doesn't imply that x you declared will have abs as its method.
I think that claim you quoted means that MATLAB's data types are internally implemented as object-oriented classes. The double data type doesn't provide any method.
  1. class(x) returns double
  2. methodsview(x) causes an error.
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Shunchao Wu
Shunchao Wu 2011년 11월 19일
I'd like to consider double as one fundmental data type, not the so called "class", and x as a normal variable, not an object. With regard to class(x), methods(x), methodsview(x) and isobject(x), I regard them as some games.
Shunchao Wu
Shunchao Wu 2011년 11월 19일
Thank you all:)

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추가 답변 (2개)

Daniel Shub
Daniel Shub 2011년 11월 11일
I disagrees with both answers. Starting with
x = -1;
You can see that abs is a method with
methods(x)
metaclass(x)
methodsview(class(x))
Interesting, as Fangjun mentioned,
methodsview(x)
gives an error. Exploring the double class in general
?double
methodsview double
both list abs as a method.
Finally, creating a simply dummy class
classdef myClass < double
methods
function newClass = myClass(input)
newClass = newClass@double(input);
end
end
end
makes it so that
y = myClass(-1);
y.abs()
works.
  댓글 수: 1
Fangjun Jiang
Fangjun Jiang 2011년 11월 11일
+1. Interesting finding! I guess TMW has some inconsistency problem needs to be sorted out.

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Drew Weymouth
Drew Weymouth 2011년 11월 11일
Although your variable x is technically a MATLAB "class" ( double ), it does not have any methods associated with it. While MATLAB does have some built-in classes with methods (such as Audioplayer for example), most data types are basically primitive values. To get the absolute value of any scalar value, use y = abs(x). If x is a matrix, then this will take the absolute value of each component. If x is complex, then it will give the magnitude.

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