Question: plot3d wrong result

Hi,

I want to make a 3D plot of the following function of alpha and beta:

plot3d(Sum(exp(-beta*(2*x0-1)-alpha*(2*x0-1))/(Sum(Sum(exp(-beta*(4*x0*x1-2*x0-2*x1+1)-alpha*(2*x0-1)), x1 = 0 .. 1), x0 = 0 .. 1)), x0 = 0 .. 1), alpha = 0 .. 5, beta = 0 .. 5, axes = boxed, grid = [100, 100])

what I obtain is a wrong plot, because it gives a value of 0.25 for alpha=0, beta=0 when the correct result is 0.5

making a 2D plot using beta as a constant gives the correct result.

Is there a solution to this problem?

Thanks in advance.

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