Fitting curve through data set

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

[John D'Errico]

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]

its in the attachment but im not sure what u are saying are u criticizing my problem ? IF means?

[Chad Greene]

He means the attachment must have become detached.

[amberly hadden]

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

Answer 1

[Chad Greene]

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;

[amberly hadden]

thanks for guidance but didt get any plots by all these commands

[Chad Greene]

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]

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