Help using data from a trend line in my code.

Is there a way to incorporate the data from a trend line into your Matlab code without typing it manually? I'm running a system that uses a linear fit trend line from a graph, but the trend line has to be able to change. Currently, every time it changes I'm using the Basic Fitting tool to apply a linear fit, and then copying the equation of the line into my code. This process isn't very efficient though. Is there a way to get and use the linear fit equation just using the code, without going to the graph and applying a trend line every time it changes?

Answer 1

[Paul]

Use polyfit to make the fit and polyval to evaluate the fit. For example:

p = polyfit(x,y,n); % get fit parameters
f = polyval(p,x);  % the trend line

plot(x,y,'o',x,f,'-') %plot comparison

x is your x-data, y your y-data and n the order of the fit, in your case 1.

[Daniel Agin]

What is the "n" in p = polyfit(x,y,n);

[Paul]

Like i said the order of the fit. 1=linear.

[ravi]

paul sir if i want to liner equation(y=mx+c) then what will add in this code?

Answer 2

[Daniel Agin]

f is returning an array of numbers rather than a single equation. Is there a way to make it show an equation instead?

[Paul]

f is not the function but the function values at the specified x points. the values of p describe the function since they are the polynomial parameter values. A linear polynomial consists of two parameters, the slope value and the offset. p(1) is the slope and p(2) is the offset. So your equation is

    f(x) = p(1)*x + p(2)

Read http://www.mathworks.com/help/matlab/ref/polyfit.html for more info.