MATLAB: Help with linear fit

fitinterpolationlinear fitslope

Given a curve (x vs y) I need to do a linear fit but only between two points x1 and x2 of that curve. Then, I need to calculate the slope of this line. Could you suggest me the fastest way to do that? Thanks.

Best Answer

Here is one way:
x      = 0:0.05:1;                          % define data
y      = sin(x).^2;
x1     = x(10);                             % define interval
x2     = x(20);
xrange = x(find(x == x1):find(x == x2));    % pick out x and y vals in interval
yrange = y(find(x == x1):find(x == x2));
p      = polyfit(xrange, yrange, 1);        % do linear curve fit 
yfit   = polyval(p, xrange);
figure
hold on; grid; box
plot(x,y,xrange,yfit,'-r')
The first element of p is the slope of the linear curve.
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