Contour graph boundary problem

X =linspace(-4.5,4.5);
Y =linspace(-4.5,4.5);
[X,Y] = meshgrid(X,Y);
Z= 3426.8/63.3+660*X*4/3.14/4.5^4+1700*Y*4/3.14/4.5^4;
contourf(X,Y,Z)

Output is numerically correct but the structure I analyzed is in the form of a circle but in the output graph it looks like a square.How can i fix it? How can i make it circle?

[John D'Errico]

Z is the equation of a PLANE. Z is LINEAR in the variables X and Y.

Then, you generated values in a square region. Plotting a planar surface over a square region in the (X,Y) plane, so Z(X,Y). The net result of what you did will be straight, parallel lines in a square region.

Is there any reason you would expect to see a circle arise from that in any sense? NO.

MATLAB cannot read your mind, nor can I. So what did you expect to see? Are you looking to plot contours of a planar surface over a circular region? Are you thinking you want to create a paraboloid of revolution, and then plot contours of that surfce, which would indeed be circular?