how can find a point from an array where the points it follows start to decrease

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bay rem
bay rem 2016-2-17
回答： Jos (10584) 2016-2-17
i have array contains points, somehow it exist a part of this array where are decreasing ,how can i find this part, i really need a help

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采纳的回答

MHN
MHN 2016-2-17
Assumption : there is on only one decreasing region in your data points.
x = -2:0.1:6;
y = x.^3-5*x.^2+5*x-2;
D = diff(y);
decreaseStart = find(D<0,1,'first');
decreaseEnd = find(D<0,1,'last');
plot(x,y)
hold on
plot(x(decreaseStart:decreaseEnd),y(decreaseStart:decreaseEnd),'r');

更多回答（2 个）

Azzi Abdelmalek
Azzi Abdelmalek 2016-2-17
%Example
t=0:0.1:20
y=sin(t)
plot(t,y)
%---------------------
ii=diff(y)>0
jj=strfind(ii,[1 0])
tout=t(jj)
yout=y(jj)
Jos (10584)
Jos (10584) 2016-2-17
A decrease is where an element is smaller than the element before it.
A = [1 2 3 4 3 2 1]
changeInA = diff(A)
isDecreasing = changeInA < 0
whereDecreasing = find(isDecreasing) % perhaps add 1 to this

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