文章目录
展开Matlab中，可以使用movmax函数表示一组数据的移动最大值。移动最大值，由局部 k 个数据点范围内的最大值组成的数组。关于最大值函数max，可以参考：《Matlab数据处理之max最值函数的用法介绍》。
本文主要讲解movmax函数的常见用法，语法说明，以及一些相关实例。首先，给出movmax函数的帮助文档如下：
>> help movmax
movmax Moving maximum value.
Y = movmax(X,K) for a vector X and positive integer scalar K computes a
centered moving maximum by sliding a window of length K along X. Each
element of Y is the local maximum of the corresponding values of X
inside the window, with Y the same size as X. When K is even, the
window is centered about the current and previous elements of X. The
sliding window is truncated at the endpoints where there are fewer than
K elements from X to fill the window.
For N-D arrays, movmax operates along the first array dimension whose
size does not equal 1.
Y = movmax(X,[NB NF]) for a vector X and nonnegative integers NB and NF
computes a moving maximum along the length of X, returning the local
maximum of the previous NB elements, the current element, and the next
NF elements of X.
Y = movmax(...,DIM) operates along dimension DIM of X.
movmax(...,MISSING) specifies how NaN (Not-a-Number) values are treated
and can be one of the following:
'omitnan' - (default) the maximum of any window containing NaN
values is the maximum of all its non-NaN elements.
If all elements are NaN, the result is NaN.
'includenan' - the maximum of any window containing NaN values is
also NaN.
movmax(...,'Endpoints',ENDPT) controls how the maximum is calculated at
the endpoints of X, where there are not enough elements to fill the
window. ENDPT can be either a scalar numeric or logical value or one of
the following:
'shrink' - (default) compute the maximum over the number of
elements of X that are inside the window, effectively
reducing the window size to fit X at the endpoints.
'fill' - compute the maximum over the full window size,
filling missing values from X with -Inf. This is
equivalent to padding X with -Inf at the endpoints.
'discard' - compute the maximum only when the window is filled
with elements of X, discarding partial endpoint
calculations and their corresponding elements in Y.
This truncates the output; for a vector X and window
length K, Y has length LENGTH(X)-K+1.
When ENDPT is a scalar numeric or logical value, the missing elements
of X inside the window are replaced with that value and Y remains the
same size as X.
Example: Compute a 5-point centered moving maximum.
t = 1:10;
x = [4 3 1 -2 -4 -1 0 2 -2 3];
yc = movmax(x,5);
plot(t,x,t,yc);
Example: Compute a 5-point trailing moving maximum.
t = 1:10;
x = [4 3 1 -2 -4 -1 0 2 -2 3];
yt = movmax(x,[4 0]);
plot(t,x,t,yt);
Example: Compute a 5-point centered moving maximum, padding the ends of
the input with -Inf.
t = 1:10;
x = [4 3 1 -2 -4 -1 0 2 -2 3];
yp = movmax(x,5,'Endpoints','fill');
plot(t,x,t,yp);
Example: Compute a 5-point trailing moving maximum, ignoring the first
4 window shifts that do not contain 5 input elements.
x = [4 3 1 -2 -4 -1 0 2 -2 3];
yd = movmax(x,[4 0],'Endpoints','discard');movmax函数常见用法
M = movmax(A,k)
M = movmax(A,[kb kf])
M = movmax(___,dim)
M = movmax(___,nanflag)
M = movmax(___,Name,Value)movmax函数语法说明
M = movmax(A,k) 返回由局部 k 个数据点范围内的最大值组成的数组，其中每个最大值基于 A 的相邻元素的长度为 k 的移动窗口计算得出。当 k 为奇数时，窗口以当前位置的元素为中心。当 k 为偶数时，窗口以当前元素及其前一个元素为中心。当没有足够的元素填满窗口时，窗口将自动在端点处截断。当窗口被截断时，只根据窗口内的元素计算最大值。M 与 A 的大小相同。
- 如果 A 是向量，movmax 将沿该向量的长度运算。
- 如果 A 为多维数组，则 movmax 沿大小不等于 1 的第一个数组维度进行运算。
M = movmax(A,[kb kf]) 通过长度为 kb+kf+1 的窗口计算最大值，其中包括当前位置的元素、后面的 kb 个元素和前面的 kf 个元素。
M = movmax(_,dim) 为上述任意语法返回维度 dim 上的移动最大值数组。例如，如果 A 是矩阵，则 movmax(A,k,2) 沿 A 的列运算，计算每一行的 k 个元素的移动最大值。
M = movmax(_,nanflag) 指定在上述任意语法的计算中包括还是忽略 NaN 值。movmax(A,k,’includenan’) 会在计算中包括所有 NaN 值，而 movmax(A,k,’omitnan’) 则忽略这些值并基于较少的点计算最大值。
M = movmax(_,Name,Value) 使用一个或多个名称-值对组参数指定移动最大值的其他参数。例如，如果 x 是时间值向量，则 movmax(A,k,’SamplePoints’,x) 相对于 x 中的时间计算移动最大值。
movmax函数实例
向量的中心移动最大值
计算行向量的三点中心移动最大值。当端点处的窗口中少于三个元素时，将根据可用元素计算最大值。
>> A = [4 8 6 -1 -2 -3 -1 3 4 5];
>> M = movmax(A,3)
M =
8 8 8 6 -1 -1 3 4 5 5向量的尾部移动最大值
计算行向量的三点尾部移动最大值。当端点处的窗口中少于三个元素时，movmax 将根据可用元素的数量计算最大值。
>> A = [4 8 6 -1 -2 -3 -1 3 4 5];
>> M = movmax(A,[2 0])
M =
4 8 8 8 6 -1 -1 3 4 5矩阵的移动最大值
计算矩阵中每行的三点中心移动最大值。窗口从第一行开始，沿水平方向移动到该行的末尾，然后移到第二行，依此类推。维度参数为 2，即跨 A 的列移动窗口。
>> A = [4 8 6; -1 -2 -3; -1 3 4]
A =
4 8 6
-1 -2 -3
-1 3 4
>> M = movmax(A,3,2)
M =
8 8 8
-1 -1 -2
3 4 4
包含 NaN 元素的向量的移动最大值
计算包含两个 NaN 元素的行向量的三点中心移动最大值。
>> A = [4 8 NaN -1 -2 -3 NaN 3 4 5];
>> M = movmax(A,3)
M =
8 8 8 -1 -1 -2 3 4 5 5重新计算最大值，但包括 NaN 值。当计算包含至少一个 NaN 值的一组元素的最大值时，movmax 将返回 NaN。
>> M = movmax(A,3,'includenan')
M =
8 NaN NaN NaN -1 NaN NaN NaN 5 5基于样本点计算移动最大值
根据时间向量 t，计算 A 中数据的 3 小时中心移动最大值。
>> A = [4 8 6 -1 -2 -3];
>> k = hours(3);
>> t = datetime(2016,1,1,0,0,0) + hours(0:5)
t =
1 至 5 列
2016-01-01 00:00:00 2016-01-01 01:00:00 2016-01-01 02:00:00 2016-01-01 03:00:00 2016-01-01 04:00:00
6 列
2016-01-01 05:00:00>> M = movmax(A,k,'SamplePoints',t)
错误使用 movmax
窗口长度必须为有限标量正整数，或者为包含有限非负整数的 2 元矢量。版本问题报错了，我用的2016版本，以下为官网给的结果
>> M = movmax(A,k,'SamplePoints',t)
M = 1×6
8 8 8 6 -1 -2
仅返回满窗口最大值
计算行向量的三点中心移动最大值，但在输出中舍弃使用的点数少于三个的计算。也就是说，只返回从满的三元素窗口计算的最大值，而舍弃端点计算。
>> A = [4 8 6 -1 -2 -3 -1 3 4 5];
>> M = movmax(A,3,'Endpoints','discard')
M =
8 8 6 -1 -1 3 4 5原创文章，作者：古哥
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