Help using data from a trend line in my code.

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Daniel Agin
Daniel Agin 2014-1-17
评论： ravi 2014-4-25
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?

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回答（2 个）

Paul
Paul 2014-1-18
编辑：Paul 2014-1-18
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
Daniel Agin 2014-1-21
f is returning an array of numbers rather than a single equation. Is there a way to make it show an equation instead?
  1 个评论
Paul
Paul 2014-1-21
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.

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