Taking gradient of solution and plotting results in very weird and unsmooth graphs?

Question

Mark Lepage 2018-3-8

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https://ww2.mathworks.cn/matlabcentral/answers/386989-taking-gradient-of-solution-and-plotting-results-in-very-weird-and-unsmooth-graphs

回答： Ravi Kumar 2018-3-8

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Hello,

So I am interpolating a PDE solution to a meshgrid, and then taking the gradient of this.

When I plot the resulting gradient as a contour plot, I am getting extremely weird graphs in attachment (attached).

The gradient should be smooth (it is a gradient of a conservative potential field).

Any ideas what I am doing wrong?? Here is my pseudo code:

%interpolate PDE result
[X,Y,Z] = meshgrid(-(diam-1):diam,-(diam-1):diam,-(height-1):height);
V = interpolateSolution(result,X,Y,Z);
V = reshape(V,size(X));
%Calculate gradient
[Ex,Ey,Ez] = gradient(V);
Ex = -Ex;
Ey = -Ey;
Ez = -Ez;
    %Slice and plot z slice vectors
 sliceEx = Ex(xslice,:,:);
 figure, contourf(sliceEx,50)