;----define the gamma distribution
function gamma_fit, shape, slope, N0, r
  return, N0*r^shape*exp(-slope*r)/gamma(shape+1)
end

;
;----------------fitting----------------
;provide an initial guess of the functions parameters
initial=[7,1,1.e8]
weights=0
x=FLOAT(INDGEN(10))
y=[12.0, 11.0, 10.2, 9.4, 8.7, 8.1, 7.5, 6.9, 6.5, 6.1]
yfit = CURVEFIT(x, y, weights, initial, SIGMA, FUNCTION_NAME='gamma_fit')


END