FUNCTION MSEmatch,x,y
;+
;p=MSEmatch(x,y) provides a vector p=[a,b] such that
;mean-squared difference between x and (ay+b) is minimized.
;-
IF N_PARAMS() LT 2 THEN Message,'Incorrect number of input vectors',/Error

IF N_Elements(x) NE N_Elements(y) THEN $
   Message,'Vectors must be of equal length',/Error

;Compute the various mean values needed to calculate the
;parameters
n=N_Elements(x)
xbar=Total(x)/n
ybar=Total(y)/n
xybar=Total(x*y)/n
y2bar=Total(y^2)/n

a=(xybar-xbar*ybar)/(y2bar-ybar^2)
b=xbar-a*ybar
Return,[a,b]
END