Fitting curve through data set

2014 6 9
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更新时间：2014 6 11
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Hi Im interested to plot XY which is a curve also Im interested to fit a best fit curve through data which should follow the data trend as is and then the point from where curve is changing or having maximum curvature, (X-value at that point) and a best fit line from the trend where values are straight to get intercept, After getting intercept I would like to use intercept and slop to draw another model on same graph. please see the attached figure for detailed idea.
Guide me please Thank you

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John D'Errico
John D'Errico 2014-6-9
编辑：John D'Errico 2014-6-9
What attached figure? I might suggest my SLM toolbox for something like this, but I do not understand what you are asking. A picture really is worth 1000 words. At least, it is IF you do give us the picture. :)
amberly hadden
amberly hadden 2014-6-9
its in the attachment but im not sure what u are saying are u criticizing my problem ? IF means?
Chad Greene
Chad Greene 2014-6-9
He means the attachment must have become detached.
amberly hadden
amberly hadden 2014-6-10
Alright, here are details.
I'm interested to get a plot of X-Y, then I want to draw a curve which passes through the data set a smooth curve. Then at maximum curvature or at point where the curve is changing the trend want value of x- at that point and then want to draw a straight line which passes through the maximum data (best fit) to get the intercept and slop. Now i would like to plot another daata set on same plot....
Hopefully now you have got my idea.
Thanks jay

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Chad Greene
Chad Greene 2014-6-9

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Given data at x and y, if you want a ytrend = m(xtrend) + b slope intercept form of the trend line, you can get it by
P = polyfit(x,y,1);
m = P(1);
b = P(2);
Make up some x values for the trend line:
xtrend = min(x):max(x);
Now the trend line is
ytrend = m*xtrend + b;

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amberly hadden
amberly hadden 2014-6-10
thanks for guidance but didt get any plots by all these commands
Chad Greene
Chad Greene 2014-6-10
The steps above only calculate the trendline. After you've calculated the trend line, try
plot(x,y,'ro'); % plots your original data
hold on; % allows you to plot more data
plot(xtrend,ytrend,'k-') % plots the trend line
amberly hadden
amberly hadden 2014-6-11
Hi Chad,
Thank you. I didt see any curve passing through data or any trend line no slop and intercept.
Please guide lil more
Regards Jay

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