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# functions in yeti_fit_2d_spike.i - f

 fit_2d_spike ``` Parameters: A(1) = peak intensity of spike A(2) = FWHM of spike A(3) = abscissa of spike A(4) = ordinate of spike A(5) = background level A(6) = background X-slope A(7) = background Y-slope Model: MODEL(X,Y) = A1*P((X-A3)/A2)*P((Y-A4)/A2) + A5 + A6*(X-A3) + A7*(Y-A4) where P(U) is the shape function. SHAPE is the 1-D shape of the spike, it can be "spline" to use a cubic B-spline function, "gauss" to use a gaussian or any user defined routine which has the following prototype: func SHAPE(&p, &dp, u) {gg_fit_2d_spike(data) p = f(u); dp = f'(u); } where f(u) is a "bell-shaped" function and f'(u) is its derivative; f(u) should have with the following properties: f(0) = 1 f(0.5) = 0.5 f(-u) = f(u) (i.e. f is symmetric) f(u) >= 0 everywhere f'(u)>0 for u<0, f'(0)=0, f'(u)<0 for u>0 (i.e. f is "bell-shaped") the 3 first properties are needed to properly define the FWHM (Full Half Width at Half Maximum). Background: BG = nil/0 no background (BG = 0 everywhere) BG = 1 uniform background BG = 2 BG(x,y) = a() + a()*(x-x0) + a()*(y-y0) Spike: Support: */ interpreted function, defined at contrib/yeti_fit_2d_spike.i line 385 ```