[EMAIL PROTECTED] (Joe Ward) SHOUTED in message news:<[EMAIL PROTECTED]>... [snipped] > ----- Original Message ----- > From: "Robert J. MacG. Dawson" <[EMAIL PROTECTED]> > To: "Anders" <[EMAIL PROTECTED]> > > > Anders wrote: > > > > > > I am using the least-mean-square method to calculate the best straight > > > line to a number of meassured points. But how do I change the formulas > > > if I want one of my meassured points to be fixed (the line must go > > > throu that point). This is possible in Excel, but only to fix the > > > y-value at x=0. I presume it is mathematically possible but havn't > > > found any formula for it. > >
If you mean to do it in Excel, let's assume you want the line to go through the point x0,y0. Then compute x* = x - x0 and y* = y - y0. Now fit your no-intercept line. Let's say the slope coefficient is 'b'. Then your fitted line is (y - y0) = b(x - x0) + e. If you wish, you can then re-arrange that to y = [y0 - b x0] + bx + e. You can fit it by hand quite easily - the estimated coefficient is b = Sxy/Sxx where here Sxy = Sum[x*(i).y*(i)], Sxx = Sum[x*(i)^2] Glen . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
