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When I try to plot the DSolve output, I get empty plot.

Here is the code

Eq1 = -(r + k)/k*(1 + 1/beta)*D[(D[u[r], r] - (u[r] + 1)/(r + k)), r] == p
bcs1 =  u[-1] == 1;
bcs2 = u[1] == 1;
sol = DSolve[{Eq1, bcs1, bcs2}, u[r], r]
k = 0.1; beta = 0.1; p = 0.1;
Plot[u[r] /. sol, {r, -1, 1}]

I have no idea where, I made a mistake.

Please guide me.

Thanks

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    $\begingroup$ When something won't plot, it's useful to look at the numerical values. ThingThatWontPlot/.variable->SomeSensibleValue//N $\endgroup$
    – John Doty
    Commented Jun 9, 2015 at 16:20

1 Answer 1

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One way to see the problem, is to evaluate the solution, using Table for some values:

 Chop@Table[u[r] /. sol, {r, -1, 1, .1}]

Mathematica graphics

So the solution is complex valued. So to plot it, use Re and Im

 Plot[Re[u[r] /. sol], {r, -1, 1}]

Mathematica graphics

 Plot[Im[u[r] /. sol], {r, -1, 1}]

Mathematica graphics

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