### Division by zero error when plotting a gradient

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What I want to do is plot `\gradient\lnorm\nabla u\rnorm_2^2`, where `u` is the solution to my PDE:

When I run this code, I get:

solve(a == L, u, bc)

v = dot(grad(u), grad(u))

plot(grad(v))

When I run this code, I get:

/usr/lib/python2.7/dist-packages/matplotlib/quiver.py:645: RuntimeWarning: divide by zero encountered in double_scalars

length = a * (widthu_per_lenu / (self.scale * self.width))

/usr/lib/python2.7/dist-packages/matplotlib/quiver.py:645: RuntimeWarning: invalid value encountered in multiply

length = a * (widthu_per_lenu / (self.scale * self.width))

The problem is with plotting, and not computing the gradient. Just calling grad(u) on its own causes no error.

The problem is with plotting, and not computing the gradient. Just calling grad(u) on its own causes no error.

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