15.37.11  DGAUSSIAN   

Does a fit to:
     Z=a0*EXP(-0.5*(((X-a1)/a2)**2)+((Y-a3)/a4)**2))[+a5+a6*X+a7*Y]    for
NONLINEAR=ON (Default) or
     for data points with Y>0.0.

If  you specify NTERMS=n where n is larger than 5 a Dpolynomial background
is added to the gaussian.  The number of terms in the background  is  n-5.
If NTERMS=6,8 a constant, or sloped plane is used for the background.