Jay Warner wrote:
>
> Simplest approach would be to transform the x-axis data so that the
> desired fixed point was at x = 0, and transform the y-axis so the desired
> fixed point was at 0, then tell Excel to force the line to go through
> (x,y) = (0,0).
>
> You can do this by subracting (or adding) a fixed value to the x's and
> another fixed value to the y's.
Another way of getting this result would be to use weighted regression
and put a very high weight on the point you wanted to be sure to hit, or
(if Excel doesn't support weighted regression) to cut and paste 1000
copies of the point you want to hit into the data set.
But this misses the question that I was trying to raise: why is it
desirable to do this? Most natural situations in which one would take
it for granted that f(a) = b would also be such that you would take it
for granted that Var(f(x)) is less for x near a than for x far from a.
In such a case you might do better to subtract (a,b) from each vector
and do a log-log transform.
The question as asked doesn't give enough information to justify an
answer yet. More information is needed.
-RD
.
.
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