Finding local minima about either side of a maxima in a matrix in matlab

For some "big data" processing. When plotted my data is sign wave like but with random peaks. (So imagine plotting the value of each matrix position against it's position)

I know how to find the peaks, but I need a way of then finding the value of local minima either side of the peaks and the position in the matrix. For example, if the data were:

3 2 1 0 1 2 3 7 -4 -5 -6 -5 -4 0

The function I need would return something like: min,loc = [0, -6; 4, 11]

asked Nov 14 '18 at 13:49

user2587726

2327

So if you know how to find peaks in a vector x, to find the minima just find the peaks of -x.

– obchardon
Nov 14 '18 at 14:09

add a comment |

For some "big data" processing. When plotted my data is sign wave like but with random peaks. (So imagine plotting the value of each matrix position against it's position)

I know how to find the peaks, but I need a way of then finding the value of local minima either side of the peaks and the position in the matrix. For example, if the data were:

3 2 1 0 1 2 3 7 -4 -5 -6 -5 -4 0

The function I need would return something like: min,loc = [0, -6; 4, 11]

asked Nov 14 '18 at 13:49

user2587726

2327

So if you know how to find peaks in a vector x, to find the minima just find the peaks of -x.

– obchardon
Nov 14 '18 at 14:09

add a comment |

For some "big data" processing. When plotted my data is sign wave like but with random peaks. (So imagine plotting the value of each matrix position against it's position)

I know how to find the peaks, but I need a way of then finding the value of local minima either side of the peaks and the position in the matrix. For example, if the data were:

3 2 1 0 1 2 3 7 -4 -5 -6 -5 -4 0

The function I need would return something like: min,loc = [0, -6; 4, 11]

asked Nov 14 '18 at 13:49

user2587726

2327

For some "big data" processing. When plotted my data is sign wave like but with random peaks. (So imagine plotting the value of each matrix position against it's position)

I know how to find the peaks, but I need a way of then finding the value of local minima either side of the peaks and the position in the matrix. For example, if the data were:

3 2 1 0 1 2 3 7 -4 -5 -6 -5 -4 0

The function I need would return something like: min,loc = [0, -6; 4, 11]

matlab max min minima

asked Nov 14 '18 at 13:49

user2587726

2327

asked Nov 14 '18 at 13:49

user2587726

2327

asked Nov 14 '18 at 13:49

user2587726

2327

asked Nov 14 '18 at 13:49

user2587726

2327

asked Nov 14 '18 at 13:49

user2587726

2327

So if you know how to find peaks in a vector x, to find the minima just find the peaks of -x.

– obchardon
Nov 14 '18 at 14:09

add a comment |

So if you know how to find peaks in a vector x, to find the minima just find the peaks of -x.

– obchardon
Nov 14 '18 at 14:09

So if you know how to find peaks in a vector x, to find the minima just find the peaks of -x.

– obchardon
Nov 14 '18 at 14:09

add a comment |

2 Answers
2

active

oldest

votes

If you have access to R2017b or later, check out the islocalmax and islocalmin functions.

answered Nov 14 '18 at 14:27

CKT

72645

I'm stuck as a 2017a pleb right now :/

– user2587726
Nov 15 '18 at 10:40

add a comment |

MATLAB R2007a and newer have a function called findpeaks (which requires the Signal Processing Toolbox). The syntax that you're looking for is

[pks,locs] = findpeaks(data)

Specifically,

>> [pks,locs] = findpeaks(-[3 2 1 0 1 2 3 7 -4 -5 -6 -5 -4 0]) % note it's "-[data]"



pks =

     0     6

locs =

     4    11

The minus is because we want the "valleys" and not "peaks", so make sure you don't forget to negate pks afterwards.

answered Nov 14 '18 at 16:18

Dev-iL

17.2k64377

Whilst findpeaks works for this example, my actual data is much longer and this doesn't work I'm afraid (My apologies for not making this clear in my original question). Imagine the data were: A = [-9 3 2 1 0 1 2 3 7 -4 -5 -6 -5 -4 0 -9]; Then findpeaks(-A) would find the -9's, not the 0 and -6.

– user2587726
Nov 15 '18 at 10:23

@user2587726 you can configure the "prominence" of the extrema that findpeaks returns. See here. Also, you can use sign(diff(data)), then look for [-1 1] in the resulting vector.

– Dev-iL
Nov 15 '18 at 16:01

I'm confused about why you say findpeaks wouldn't find the 0 and -6. By default, it will (actually in the example you gave it won't find the -9 because they are on the ends). When I try this, I get peaks of 0 and 6 at locations 5 and 12 (which you'd then negate). If you also want the endpoints, just add -inf to both ends of the input.

– CKT
Nov 15 '18 at 17:53

add a comment |

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

If you have access to R2017b or later, check out the islocalmax and islocalmin functions.

answered Nov 14 '18 at 14:27

CKT

72645

I'm stuck as a 2017a pleb right now :/

– user2587726
Nov 15 '18 at 10:40

add a comment |

If you have access to R2017b or later, check out the islocalmax and islocalmin functions.

answered Nov 14 '18 at 14:27

CKT

72645

I'm stuck as a 2017a pleb right now :/

– user2587726
Nov 15 '18 at 10:40

add a comment |

If you have access to R2017b or later, check out the islocalmax and islocalmin functions.

answered Nov 14 '18 at 14:27

CKT

72645

If you have access to R2017b or later, check out the islocalmax and islocalmin functions.

answered Nov 14 '18 at 14:27

CKT

72645

answered Nov 14 '18 at 14:27

CKT

72645

answered Nov 14 '18 at 14:27

CKT

72645

answered Nov 14 '18 at 14:27

CKT

72645

I'm stuck as a 2017a pleb right now :/

– user2587726
Nov 15 '18 at 10:40

add a comment |

I'm stuck as a 2017a pleb right now :/

– user2587726
Nov 15 '18 at 10:40

I'm stuck as a 2017a pleb right now :/

– user2587726
Nov 15 '18 at 10:40

add a comment |

MATLAB R2007a and newer have a function called findpeaks (which requires the Signal Processing Toolbox). The syntax that you're looking for is

[pks,locs] = findpeaks(data)

Specifically,

>> [pks,locs] = findpeaks(-[3 2 1 0 1 2 3 7 -4 -5 -6 -5 -4 0]) % note it's "-[data]"



pks =

     0     6

locs =

     4    11

The minus is because we want the "valleys" and not "peaks", so make sure you don't forget to negate pks afterwards.

answered Nov 14 '18 at 16:18

Dev-iL

17.2k64377

Whilst findpeaks works for this example, my actual data is much longer and this doesn't work I'm afraid (My apologies for not making this clear in my original question). Imagine the data were: A = [-9 3 2 1 0 1 2 3 7 -4 -5 -6 -5 -4 0 -9]; Then findpeaks(-A) would find the -9's, not the 0 and -6.

– user2587726
Nov 15 '18 at 10:23

@user2587726 you can configure the "prominence" of the extrema that findpeaks returns. See here. Also, you can use sign(diff(data)), then look for [-1 1] in the resulting vector.

– Dev-iL
Nov 15 '18 at 16:01

I'm confused about why you say findpeaks wouldn't find the 0 and -6. By default, it will (actually in the example you gave it won't find the -9 because they are on the ends). When I try this, I get peaks of 0 and 6 at locations 5 and 12 (which you'd then negate). If you also want the endpoints, just add -inf to both ends of the input.

– CKT
Nov 15 '18 at 17:53

add a comment |

MATLAB R2007a and newer have a function called findpeaks (which requires the Signal Processing Toolbox). The syntax that you're looking for is

[pks,locs] = findpeaks(data)

Specifically,

>> [pks,locs] = findpeaks(-[3 2 1 0 1 2 3 7 -4 -5 -6 -5 -4 0]) % note it's "-[data]"



pks =

     0     6

locs =

     4    11

The minus is because we want the "valleys" and not "peaks", so make sure you don't forget to negate pks afterwards.

answered Nov 14 '18 at 16:18

Dev-iL

17.2k64377

Whilst findpeaks works for this example, my actual data is much longer and this doesn't work I'm afraid (My apologies for not making this clear in my original question). Imagine the data were: A = [-9 3 2 1 0 1 2 3 7 -4 -5 -6 -5 -4 0 -9]; Then findpeaks(-A) would find the -9's, not the 0 and -6.

– user2587726
Nov 15 '18 at 10:23

@user2587726 you can configure the "prominence" of the extrema that findpeaks returns. See here. Also, you can use sign(diff(data)), then look for [-1 1] in the resulting vector.

– Dev-iL
Nov 15 '18 at 16:01

I'm confused about why you say findpeaks wouldn't find the 0 and -6. By default, it will (actually in the example you gave it won't find the -9 because they are on the ends). When I try this, I get peaks of 0 and 6 at locations 5 and 12 (which you'd then negate). If you also want the endpoints, just add -inf to both ends of the input.

– CKT
Nov 15 '18 at 17:53

add a comment |

MATLAB R2007a and newer have a function called findpeaks (which requires the Signal Processing Toolbox). The syntax that you're looking for is

[pks,locs] = findpeaks(data)

Specifically,

>> [pks,locs] = findpeaks(-[3 2 1 0 1 2 3 7 -4 -5 -6 -5 -4 0]) % note it's "-[data]"



pks =

     0     6

locs =

     4    11

The minus is because we want the "valleys" and not "peaks", so make sure you don't forget to negate pks afterwards.

answered Nov 14 '18 at 16:18

Dev-iL

17.2k64377

MATLAB R2007a and newer have a function called findpeaks (which requires the Signal Processing Toolbox). The syntax that you're looking for is

[pks,locs] = findpeaks(data)

Specifically,

>> [pks,locs] = findpeaks(-[3 2 1 0 1 2 3 7 -4 -5 -6 -5 -4 0]) % note it's "-[data]"



pks =

     0     6

locs =

     4    11

The minus is because we want the "valleys" and not "peaks", so make sure you don't forget to negate pks afterwards.

answered Nov 14 '18 at 16:18

Dev-iL

17.2k64377

answered Nov 14 '18 at 16:18

Dev-iL

17.2k64377

answered Nov 14 '18 at 16:18

Dev-iL

17.2k64377

answered Nov 14 '18 at 16:18

Dev-iL

17.2k64377

Whilst findpeaks works for this example, my actual data is much longer and this doesn't work I'm afraid (My apologies for not making this clear in my original question). Imagine the data were: A = [-9 3 2 1 0 1 2 3 7 -4 -5 -6 -5 -4 0 -9]; Then findpeaks(-A) would find the -9's, not the 0 and -6.

– user2587726
Nov 15 '18 at 10:23

@user2587726 you can configure the "prominence" of the extrema that findpeaks returns. See here. Also, you can use sign(diff(data)), then look for [-1 1] in the resulting vector.

– Dev-iL
Nov 15 '18 at 16:01

I'm confused about why you say findpeaks wouldn't find the 0 and -6. By default, it will (actually in the example you gave it won't find the -9 because they are on the ends). When I try this, I get peaks of 0 and 6 at locations 5 and 12 (which you'd then negate). If you also want the endpoints, just add -inf to both ends of the input.

– CKT
Nov 15 '18 at 17:53

add a comment |

Whilst findpeaks works for this example, my actual data is much longer and this doesn't work I'm afraid (My apologies for not making this clear in my original question). Imagine the data were: A = [-9 3 2 1 0 1 2 3 7 -4 -5 -6 -5 -4 0 -9]; Then findpeaks(-A) would find the -9's, not the 0 and -6.

– user2587726
Nov 15 '18 at 10:23

@user2587726 you can configure the "prominence" of the extrema that findpeaks returns. See here. Also, you can use sign(diff(data)), then look for [-1 1] in the resulting vector.

– Dev-iL
Nov 15 '18 at 16:01

I'm confused about why you say findpeaks wouldn't find the 0 and -6. By default, it will (actually in the example you gave it won't find the -9 because they are on the ends). When I try this, I get peaks of 0 and 6 at locations 5 and 12 (which you'd then negate). If you also want the endpoints, just add -inf to both ends of the input.

– CKT
Nov 15 '18 at 17:53

Whilst findpeaks works for this example, my actual data is much longer and this doesn't work I'm afraid (My apologies for not making this clear in my original question). Imagine the data were: A = [-9 3 2 1 0 1 2 3 7 -4 -5 -6 -5 -4 0 -9]; Then findpeaks(-A) would find the -9's, not the 0 and -6.

– user2587726
Nov 15 '18 at 10:23

@user2587726 you can configure the "prominence" of the extrema that findpeaks returns. See here. Also, you can use sign(diff(data)), then look for [-1 1] in the resulting vector.

– Dev-iL
Nov 15 '18 at 16:01

I'm confused about why you say findpeaks wouldn't find the 0 and -6. By default, it will (actually in the example you gave it won't find the -9 because they are on the ends). When I try this, I get peaks of 0 and 6 at locations 5 and 12 (which you'd then negate). If you also want the endpoints, just add -inf to both ends of the input.

– CKT
Nov 15 '18 at 17:53

add a comment |

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