matlab plot three different colors for three different change (red, yellow, blue)

Question

K.E. 2017-7-17

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https://ww2.mathworks.cn/matlabcentral/answers/348994-matlab-plot-three-different-colors-for-three-different-change-red-yellow-blue

编辑： Stephen23 2017-7-17

在 MATLAB Online 中打开

In https://www.amcharts.com/demos/line-different-colors-ups-downs/ ,

it describes plotting different colors for up and downs. How can I do the same for matlab? I attach an example

plot([1 2 3 4 5 6 7 8 9 10], [5 5 7 5 2 5 5 8 9 2])

which involves no change as well. I want to have yellow for ups and blue for downs, and red for no change.

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Answer 1

KSSV 2017-7-17

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x = [1 2 3 4 5 6 7 8 9 10] ;
y = [5 5 7 5 2 5 5 8 9 2] ;
figure
hold on
for i = 1:length(x)-1
   m = (y(i)-y(i+1))/(x(i)-x(i+1)) ;
   if sign(m)==0
        plot(x(i:i+1),y(i:i+1),'r') ;
   elseif sign(m)==-1
        plot(x(i:i+1),y(i:i+1),'b') ;
   elseif sign(m)==1
        plot(x(i:i+1),y(i:i+1),'y') ;
   end
end

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Answer 2

Stephen23 2017-7-17

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https://ww2.mathworks.cn/matlabcentral/answers/348994-matlab-plot-three-different-colors-for-three-different-change-red-yellow-blue#answer_274379

编辑：Stephen23 2017-7-17

在 MATLAB Online 中打开

This is MATLAB, so there is no need to use ugly loops or write complicated code. Simple is always best.

X = [1,2,3,4,5,6,7,8,9,10];
Y = [5,5,7,5,2,5,5,8,9,2];
D = [NaN,diff(Y),NaN]
idz = D(1:end-1)==0 | D(2:end)==0;
idp = D(1:end-1)>0  | D(2:end)>0;
idn = D(1:end-1)<0  | D(2:end)<0;
plot(X,Y+0./idz,'r', X,Y+0./idp,'y', X,Y+0./idn,'b')