How to find the coordinates of starting, end point and peak from graph?

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parag gupta 2019-8-2

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https://ww2.mathworks.cn/matlabcentral/answers/474582-how-to-find-the-coordinates-of-starting-end-point-and-peak-from-graph

评论： Star Strider 2019-8-3

采纳的回答： Star Strider

How to find the peak value, end point and distance between starting and end point?

x = linespace(-5,5); y = sqrt((36-x.^2)/9); figure() plot (x,y)

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Star Strider 2019-8-2

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https://ww2.mathworks.cn/matlabcentral/answers/474582-how-to-find-the-coordinates-of-starting-end-point-and-peak-from-graph#answer_385930

在 MATLAB Online 中打开

Try this:

x = linspace(-5,5);
y = sqrt((36-x.^2)/9);
figure()
plot (x,y)
[onePeak,loc] = max(y)                          % Peak Value & Index
endPoint = y(end)                               % End Point Value
se_dist = max(x) - min(x)                       % Start To End Distance

producing:

onePeak =
    1.9999
loc =
    50
endPoint =
    1.1055
se_dist =
    10

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Star Strider 2019-8-2

在 MATLAB Online 中打开

I’ve not written an event function for a delay differential equation solver before, largely because I rarely use delay differential equations (and have not in a while).

Try this:

function v = funtryp(t,y,Z);
r_v = 0.33; r_l = 0.33;b1 = 2*10^(-9);b3 = 0.5;t2 = 10;d_v = 0.5;d_l = 0.5;d_m = 0.1;c = 10^(2);       
C = 10^(8);gamma = 2.71;delta = 2.5*10^(-2);b2 = 0.15;
ylag1 = Z(:,1); x = 1;b2 = 0.15;
v = zeros(5,1);
v(1) = r_v*y(1)-b1*y(4)*y(1)-b2*y(1)-d_v*y(5)*y(1);
v(2) = r_l*y(2)+b1*y(4)*y(1)+b2*y(1)-gamma*y(2)-d_l*y(5)*y(2);
v(3) = gamma*y(2)-delta*y(3)-d_m*y(5)*y(3);
v(4) =y(1)+y(2)-b3*y(4);
v(5) = c*(((ylag1(1)+ylag1(2)+ylag1(3))/C)^x)*(1-y(5));
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% runfile
function [position,isterminal,direction] = trypevents(t,y,ydel)
position = y(1)-1E-2                            % Zero Value - Threshold
isterminal = 1;
direction = 0;
end
options = ddeset('RelTol',1e-5,'AbsTol',1e-8,'InitialY',[20,0,0,0,0], 'Events',@trypevents);
sol = dde23(@(t,y,Z)funtryp(t,y,Z),100,[0,0,0,0,0],[0,1500],options);
Q1 = sol.x
Q2 = sol.y
figure();
x1 = sol.x;
y1 = sol.y(1,:);
semilogy(x1,y1,'g','LineWidth',2); hold on;
xlabel('time t');
ylabel('v1(t)');

This runs without error in R2019a, and appears to give the correct result. The syntax you posted does not run in R2019a, so you may have to adapt my code to your version. I am using semilogy for the plot to be certain the event funciton returns the correct result. Change the event threshold value (that is here 1E-002, or eliminate it entirely) to produce the result you want.

parag gupta 2019-8-3