Calculating cross-point within a set of x & y data

Question

Sonoma Rich 2011-7-20

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/12044-calculating-cross-point-within-a-set-of-x-y-data

I have a set of x & y data that I collected from a test. The plot of the data resembles a mountain with a single peak. Given this set of data, I want to calculate the values for x where y is 98% of the peak (max) value. There are two values for x. Any suggestions.

x =

y =

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Answer 1

Sean de Wolski 2011-7-20

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/12044-calculating-cross-point-within-a-set-of-x-y-data#answer_16493

在 MATLAB Online 中打开

[mxy idx] = max(y); %max and index
y98 = 0.98*mxy;  %value of y crossing
pt1 = interp1(y(1:idx),x(1:idx),y98);  %interp lower value
pt2 = interp1(y(idx:end),x(idx:end),y98); %interp higher value
plot(x,y,'b-',[pt1 pt2],[y98 y98],'gd') %visualize

Edit for multiple x-ings Per comments:

x = cumsum(repmat(x,3,1));  %sample data your x/y from before
y = repmat(y,3,1);
y98 = 0.98*max(y);
yxing = y-y98;  %zero the yvalue
ylox  = find(diff(sign(yxing))); %crossings
ylox(:,2) = ylox+1; %both sides
ylox = ylox(:);
xvals = reshape(x(ylox),[],2); %set up poits
yvals = reshape(y(ylox),[],2);
n = size(xvals,1);
xings = zeros(n,1);
for ii = 1:n
  xings(ii) = interp1(yvals(ii,:),xvals(ii,:),y98);  %interp each point
end    
plot(x,y,'b-',xings,y98,'gd') %visualzie