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movmin

Moving minimum

Description

example

M = movmin(A,k) returns an array of local k-point centered minimum values, where each minimum is calculated over a sliding window of length k across neighboring elements of A. When k is odd, the window is centered about the element in the current position. When k is even, the window is centered about the current and previous elements. The window size is automatically truncated at the endpoints when there are not enough elements to fill the window. When the window is truncated, the minimum is taken over only the elements that fill the window. M is the same size as A.

  • If A is a vector, then movmin operates along the length of the vector A.

  • If A is a multidimensional array, then movmin operates along the first dimension of A whose size does not equal 1.

example

M = movmin(A,[kb kf]) computes the minimum with a window of length kb+kf+1 that includes the element in the current position, kb elements backward, and kf elements forward.

example

M = movmin(___,dim) specifies the dimension of A to operate along for any of the previous syntaxes. For example, if A is a matrix, then movmin(A,k,2) operates along the columns of A, computing the k-element sliding minimum for each row.

example

M = movmin(___,nanflag) specifies whether to include or omit NaN values from the calculation for any of the previous syntaxes. movmin(A,k,'includenan') includes all NaN values in the calculation while movmin(A,k,'omitnan') ignores them and computes the minimum over fewer points.

example

M = movmin(___,Name,Value) specifies additional parameters for the minimum using one or more name-value pair arguments. For example, if x is a vector of time values, then movmin(A,k,'SamplePoints',x) computes the moving minimum relative to the times in x.

Examples

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Compute the three-point centered moving minimum of a row vector. When there are fewer than three elements in the window at the endpoints, take the minimum over the elements that are available.

A = [4 8 6 -1 -2 -3 -1 3 4 5];
M = movmin(A,3)
M = 1×10

     4     4    -1    -2    -3    -3    -3    -1     3     4

Compute the three-point trailing moving minimum of a row vector. When there are fewer than three elements in the window at the endpoints, take the minimum over the elements that are available.

A = [4 8 6 -1 -2 -3 -1 3 4 5];
M = movmin(A,[2 0])
M = 1×10

     4     4     4    -1    -2    -3    -3    -3    -1     3

Compute the three-point centered moving minimum for each row of a matrix. The window starts on the first row, slides horizontally to the end of the row, then moves to the second row, and so on. The dimension argument is two, which slides the window across the columns of A.

A = [4 8 6; -1 -2 -3; -1 3 4]
A = 3×3

     4     8     6
    -1    -2    -3
    -1     3     4

M = movmin(A,3,2)
M = 3×3

     4     4     6
    -2    -3    -3
    -1    -1     3

Compute the three-point centered moving minimum of a row vector containing two NaN elements.

A = [4 8 NaN -1 -2 -3 NaN 3 4 5];
M = movmin(A,3)
M = 1×10

     4     4    -1    -2    -3    -3    -3     3     3     4

Recalculate the minimum, but include the NaN values. When taking the minimum over a group of elements containing at least one NaN value, movmin returns NaN.

M = movmin(A,3,'includenan')
M = 1×10

     4   NaN   NaN   NaN    -3   NaN   NaN   NaN     3     4

Compute a 3-hour centered moving minimum of the data in A according to the time vector t.

A = [4 8 6 -1 -2 -3];
k = hours(3);
t = datetime(2016,1,1,0,0,0) + hours(0:5)
t = 1x6 datetime
Columns 1 through 3

   01-Jan-2016 00:00:00   01-Jan-2016 01:00:00   01-Jan-2016 02:00:00

Columns 4 through 6

   01-Jan-2016 03:00:00   01-Jan-2016 04:00:00   01-Jan-2016 05:00:00

M = movmin(A,k,'SamplePoints',t)
M = 1×6

     4     4    -1    -2    -3    -3

Compute the three-point centered moving minimum of a row vector, but discard any calculation that uses fewer than three points from the output. In other words, return only the minimums computed from a full three-element window, discarding endpoint calculations.

A = [4 8 6 -1 -2 -3 -1 3 4 5];
M = movmin(A,3,'Endpoints','discard')
M = 1×8

     4    -1    -2    -3    -3    -3    -1     3

Input Arguments

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Input array, specified as a vector, matrix, or multidimensional array.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical

Window length, specified as a numeric or duration scalar. When k is a positive integer scalar, the centered minimum includes the element in the current position plus surrounding neighbors.

For example, movmin(A,3) computes an array of local three-point minimum values.

movmin(A,3) computation. The elements in the sample window are 1, 3, and 5, so the resulting local minimum is 1.

Directional window length, specified as a numeric or duration row vector containing two elements. When kb and kf are positive integer scalars, the calculation is over kb+kf+1 elements. The calculation includes the element in the current position, kb elements before the current position, and kf elements after the current position.

For example, movmin(A,[2 1]) computes an array of local four-point minimum values.

movmin(A,[2 1]) computation. The elements in the sample window are 4, 1, 3, and 5, so the resulting local minimum is 1.

Dimension to operate along, specified as a positive integer scalar. If you do not specify the dimension, then the default is the first array dimension of size greater than 1.

Dimension dim indicates the dimension that movmin operates along, that is, the direction in which the specified window slides.

Consider an m-by-n input matrix, A:

  • movmin(A,k,1) computes the k-element sliding minimum for each column of A and returns an m-by-n matrix.

    movmin(A,k,1) column-wise operation

  • movmin(A,k,2) computes the k-element sliding minimum for each row of A and returns an m-by-n matrix.

    movmin(A,k,2) row-wise operation

NaN condition, specified as one of these values:

  • 'omitnan' — Ignore all NaN values in the input. If a window contains only NaN values, then movmin returns NaN.

  • 'includenan' — Include NaN values from the input when computing the minimum, resulting in the output NaN.

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: M = movmin(A,k,'Endpoints','fill')

Method to treat leading and trailing windows, specified as one of these options:

'Endpoints' ValueDescription
'shrink'Shrink the window size near the endpoints of the input to include only existing elements.
'discard'Do not output any minimums when the window does not completely overlap with existing elements.
'fill'Substitute nonexisting elements with -Inf.
numeric or logical scalarSubstitute nonexisting elements with a specified numeric or logical value.

Data Types: double | single | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical | char | string

Sample points for computing minimums, specified as a vector. The sample points represent the location of the data in A. Sample points do not need to be uniformly sampled. By default, the sample points vector is [1 2 3 ... ].

Moving windows are defined relative to the sample points, which must be sorted and contain unique elements. For example, if t is a vector of times corresponding to the input data, then movmin(rand(1,10),3,'SamplePoints',t) has a window that represents the time interval between t(i)-1.5 and t(i)+1.5.

When the sample points vector has data type datetime or duration, then the moving window length must have type duration.

If the sample points are nonuniformly spaced and the 'Endpoints' name-value pair is specified, then its value must be 'shrink'.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | datetime | duration

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced in R2016a

See Also

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