predicting the trends of diagram
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shahin hashemi
le 5 Juin 2018
Commenté : Image Analyst
le 6 Juin 2018
dear all
i have 2 data point like this that come from nonlinear equations :
x=[13 8 6 5.5 5 4.9 4.8 4.795 4.792 4.791 4.77 4.76 ]
y=[0.154058581114650 0.149736758736220 0.144520156929792 0.141698370356069 0.136778534431870 0.135128381143846 0.132667849050780 0.132491826080336 0.132381996482185 0.132344176545640 0.131391601025611 0.130704833218502]
plot(x,y)
and when i plot these points i got following diagram
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/191027/image.jpeg)
is there any way to predict at which point of x the y is equal to zero
thank you all
2 commentaires
Star Strider
le 5 Juin 2018
Be very careful with any extrapolation you do with these (or any other) data. The curve you posted could be part of a function that may never be close to 0.
If the points you plotted are from a deterministic equation, you do not need to interpolate. Simply calculate them.
Please do not ever extrapolate so far beyond the region of known data.
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Image Analyst
le 5 Juin 2018
You could try this:
x=[13 8 6 5.5 5 4.9 4.8 4.795 4.792 4.791 4.77 4.76 ]
y=[0.154058581114650 0.149736758736220 0.144520156929792 0.141698370356069 0.136778534431870 0.135128381143846 0.132667849050780 0.132491826080336 0.132381996482185 0.132344176545640 0.131391601025611 0.130704833218502]
plot(x,y, 'bs-')
grid on;
% Find coefficients of a line
[sortedX, sortOrder] = sort(x, 'Ascend');
sortedY = y(sortOrder);
coefficients = polyfit(sortedX(1:2), sortedY(1:2), 1);
% Line equation is y = coefficients(1) * x + coefficients(2)
% y=0 when x = -coefficients(2) / coefficients(1)
xWhenYEquals0 = -coefficients(2) / coefficients(1)
% Plot it.
hold on;
plot(xWhenYEquals0, 0, 'r*');
% Plot line from there tothe first data point.
plot([xWhenYEquals0, sortedX(1)], [0, sortedY(1)], 'r-');
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/188996/image.png)
If you want some other model, other than linear extrapolation of the left-most two points, let me know.
4 commentaires
Image Analyst
le 6 Juin 2018
Just give me an equation like y = a1 * sin(a2*x) + a3 * cos(a4*x).^2 or whatever you expect the theory to be. The a's would be the unknowns to be solved for.
Plus de réponses (1)
Image Analyst
le 5 Juin 2018
You can fit a line between the left two points and extrapolate. Or do you have some model/equation you think the whole curve follows, and if so do you have the stats toolbox?
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