Problem with region plot

I have a function f[x,y] involving numerical integration. It returns values for any values of x and y well, and if I want to plot its as a function of one of arguments with fixed remained argument it goes well.

However, when I try to compute RegionPlot[f[x,y]>=1, {x,x0,x1},{y,y0,y1}], it returns some number of errors like

NIntegrate::inumr: The integrand 0.0019697 (-E^(-((1.15633*10^18 10^Uee mN <<1>>)/EN))+E^(-((9.63608*10^17 10^Uee mN InterpolatingFunction[(0.01 35.92),<<3>>,{Automatic}][mN])/EN))) If[EN>=39\[And]EN<=117,Interpolation[hnlfromwenergydistribution,InterpolationOrder->6][EN],0] has evaluated to non-numerical values for all sampling points in the region with boundaries (Indeterminate Indeterminate).

and after all, instead of region plot the output is just False. What can be a reason for this, and how to avoid this?

• Difficult to assist without f[x,y]. Sep 22 '18 at 21:29
• Try defining f[x_?NumericQ, y_?NumericQ] := ... instead of f[x_, y_] := .... Sep 22 '18 at 21:47

It seems that you have non-numeric values like Uee and mN in the plotted function. Try evaluating f[x,y] for some values of $$x$$ and $$y$$, and if it does not return a number, you can not plot it.