[英]matlab maximum of array with unknown dimension
I would like to compute the maximum and, more importantly, its coordinates of an N-by-N...by-N array, without specifying its dimensions. 我想计算最大值,更重要的是,计算N-by-N ... by-N数组的坐标,而不指定其尺寸。
For example, let's take: 例如,我们采取:
A = [2 3];
B = [2 3; 3 4];
The function (lets call it MAXI
) should return the following values for matrix A
: 函数(让我们称之为
MAXI
)应返回矩阵A
的以下值:
[fmax, coor] = MAXI(A)
fmax =
3
coor =
2
and for matrix B
: 对于矩阵
B
:
[fmax, coor] = MAXI(B)
fmax =
4
coor=
2 2
The main problem is not to develop a code that works for one class in particular, but to develop a code that as quickly as possible works for any input (with higher dimensions). 主要问题不是开发一个特别适用于某个类的代码,而是开发一个尽可能快地适用于任何输入(具有更高维度)的代码。
To find the absolute maximum, you'll have to convert your input matrix into a column vector first and find the linear index of the greatest element, and then convert it to the coordinates with ind2sub
. 要找到绝对最大值,您必须先将输入矩阵转换为列向量,然后找到最大元素的线性索引,然后将其转换为
ind2sub
的坐标。 This can be a little bit tricky though, because ind2sub
requires specifying a known number of output variables. 这可能有点棘手,因为
ind2sub
需要指定已知数量的输出变量。 For that purpose we can employ cell arrays and comma-separated lists , like so: 为此,我们可以使用单元格数组和逗号分隔列表 ,如下所示:
[fmax, coor] = max(A(:));
if ismatrix(A)
C = cell(1:ndims(A));
[C{:}] = ind2sub(size(A), coor);
coor = cell2mat(C);
end
EDIT: I've added an additional if
statement that checks if the input is a matrix or a vector, and in case of the latter it returns the linear index itself as is. 编辑:我添加了一个额外的
if
语句,用于检查输入是矩阵还是向量,如果是后者,则返回线性索引本身。
In a function, it looks like so: 在函数中,它看起来像这样:
function [fmax, coor] = maxi(x)
[fmax, coor] = max(A(:));
if ismatrix(A)
C = cell(1:ndims(A));
[C{:}] = ind2sub(size(A), coor);
coor = cell2mat(C);
end
A = [2 3; 3 4];
[fmax, coor] = maxi(A)
fmax =
4
coor =
2 2
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