arguments block seems wrong
显示 更早的评论
the arguments block can be used to validate input arguments. Great! Except that it doesn't seem to work as advertised.
According to the documentation (doc arguments)
"The value assigned to the argument in the function call must be compatible with the specified size, or MATLAB throws an error."
However, when calling this function
function a=f(a)
arguments
a (1,3) double
end
end
with a scalar
>> f(1)
ans =
1 1 1
The function expands the erroneous scalar argument to a 3-element vector instead of casting the error that was promised!
Why would this be? Am I reading it wrong?
1 个评论
Duijnhouwer
2020-8-21
编辑：Duijnhouwer
2020-8-21
回答（1 个）
Walter Roberson
2020-8-21
0 个投票
Documented. The size of the input must be "compatible" taking into account implicit expansion.
https://www.mathworks.com/help/matlab/matlab_prog/function-argument-validation-1.html#mw_48fe4f61-8ee4-424b-ae2b-c82b8d051910
5 个评论
Duijnhouwer
2020-8-21
Walter Roberson
2020-8-21
With implicit expansion having been the rule since R2016b, compatible is probably the majority of the need now.
Duijnhouwer
2020-8-22
编辑：Duijnhouwer
2020-8-22
Bruno Luong
2020-8-22
Only scalar expansion is tolerated by ARGUMENTS, which exists in MATLAB well before R2016b
function a=f(a)
arguments
a (5,3) double
end
end
I don't know what Walter meant by implicit expansion, but the singleton expansion is not tolerated.
>> f(rand(5,3))
ans =
0.6229 0.9431 0.6980
0.2473 0.5422 0.9468
0.9195 0.5459 0.2302
0.0582 0.1777 0.2003
0.9456 0.8473 0.7904
>> f(rand(1))
ans =
0.0317 0.0317 0.0317
0.0317 0.0317 0.0317
0.0317 0.0317 0.0317
0.0317 0.0317 0.0317
0.0317 0.0317 0.0317
>> f(rand(5,1))
Error using f
Invalid argument at position 1. Value must be a matrix of size 5-by-3.
>> f(rand(1,3))
Error using f
Invalid argument at position 1. Value must be a matrix of size 5-by-3.
>>
Walter Roberson
2020-8-22
Ah, this part seems to be the key:
MATLAB indexed assignment rules apply to size specifications. For example, a 1-by-1 value is compatible with the size specified as (5,3) because MATLAB applies scalar expansion. Also, MATLAB row-column conversion applies so that a size specified as (1,:) can accept a size of 1-by-n and n-by-1.
类别
在 帮助中心 和 File Exchange 中查找有关 Creating and Concatenating Matrices 的更多信息
2020-8-21
2020-8-22
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
