What does 2nd argument mean in numel function?

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Gautam
Gautam 2015-1-8
评论： Adam 2015-1-8
Earlier version of matlab has some extra arguments for the function numel , which said, it gives the number of subscripted elements. What does it mean? I am not able to figure it out. Even the current version supports those extra arguments , but doesn't show it in Documentation. Please Explain what it is.
a = rand(5);
numel(a , 1 , 2 , 3) % it always gives 1 as output, no matter what I try
numel(a , [1 ,2]) % Gives the length of 2nd argument
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Adam
Adam 2015-1-8
subsref and subassign both use numel so maybe they make use of the further arguments in a way that is not generally useful for normal code.
I don't generally over-ride either of those two functions though in my classes as they can get complicated so I have never really looked into it.

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回答（1 个）

Guillaume
Guillaume 2015-1-8
if you do
numel(a, 1:10, 1:10)
it returns 100. It looks like it returns the product of the number of elements of all the arguments starting from the second one and actually ignores the first.
I don't see how that is useful.
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Gautam
Gautam 2015-1-8
yeah , getting it
numel(a , [2 , 3 , 6 , 8] , [3 , 2 , 9] , [1 ,2])
ans =
24
But , still what sense does it makes? There must be some usage of it. Thanks for the reply
Guillaume
Guillaume 2015-1-8
According to the earliest documentation I can find matlab used to call numel for expressions such as A{i1, i2, i3} that generate comma-separated lists, probably to know how many list elements to allocate.
I don't think it does anymore, and it looks like it's broken now as it completely ignores the size of the first argument. I would expect in the past, it would have thrown an error if the indices were out of bounds.

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