How to find x values of specified y point on the graph ?

Question

Zack Trahem 2022-7-19

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https://ww2.mathworks.cn/matlabcentral/answers/1763795-how-to-find-x-values-of-specified-y-point-on-the-graph

回答： Star Strider 2022-7-19

Let say i have two array x[1,2,3,4,5] and y[6, 7,8,9,10 ] i want to find the x values of the 6.34 on the graph. I want to put marker for that point is there any way to do it?

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Answer 1

Voss 2022-7-19

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https://ww2.mathworks.cn/matlabcentral/answers/1763795-how-to-find-x-values-of-specified-y-point-on-the-graph#answer_1011115

在 MATLAB Online 中打开

x = [1,2,3,4,5];

y = [6,7,8,9,10];

y_point = 6.34;

x_point = interp1(y,x,y_point);

plot(x,y);

hold on

plot(x_point,y_point,'r.')

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Zack Trahem 2022-7-19

graph1.fig

Thank you for quick response. this look like what i looking for. However, my y vector is not sorted in assending order and unique. I attached figure.

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Answer 2

Sam Chak 2022-7-19

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https://ww2.mathworks.cn/matlabcentral/answers/1763795-how-to-find-x-values-of-specified-y-point-on-the-graph#answer_1011120

Hi Zack,

You can use interp1 technique.

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Answer 3

Star Strider 2022-7-19

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1763795-how-to-find-x-values-of-specified-y-point-on-the-graph#answer_1011170

在 MATLAB Online 中打开

Using the supplied .fig file —

F = openfig('graph1.fig');
Lines = findobj(gca, 'Type','line');
x = Lines.XData;
y = Lines.YData;
yval = 0.0100277;                                               % Choose A Value Within tThe Range Of 'y'
yxi = find(diff(sign(y-yval)));
for k = 1:numel(yxi)
    idxrng = max(1,yxi(k)-1) : min(numel(y),yxi(k)+1);
    xv(k) = interp1(y(idxrng), x(idxrng),yval);
    yv(k) = yval;
end
% figure
% plot(x, y)
hold on
plot(xv, yv, 'rs', 'MarkerSize',10)
hold off