MATLAB: Plot surface using different x,y vector increment and got different graph

Question

Hi, I using follow code to generate a surface, got fig 1

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clear;

x=0:0.01:1;

y=0:0.01:1;

[x1,y1]=meshgrid(x,y);

z1=-1.448-0.477*x1-0.4757*y1+0.1473*x1.^2-0.1952*x1*y1+0.1334*y1.^2;

surf(x1,y1,z1,'FaceColor','red','LineStyle','none');

hold on;

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fig 1

and I change x and y vector step from 0.01 to 0.1, got fig 2

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clear;

x=0:0.1:1;

y=0:0.1:1;

[x1,y1]=meshgrid(x,y);

z1=-1.448-0.477*x1-0.4757*y1+0.1473*x1.^2-0.1952*x1*y1+0.1334*y1.^2;

surf(x1,y1,z1,'FaceColor','red','LineStyle','none');

hold on;

=========================================================

fig 2

My question is why Z-index is not same range. fig1 Z-index range is [-9,-8] and fig 2 Z-index range is [-3,-2]

which plot is correct ? and what causes this problem? How do I modify the code to produce the same plot?

Thanks….

Answer 1

Hi

In your formula, there is an operation that is not element wise:

z1=-1.448-0.477*x1-0.4757*y1+0.1473*x1.^2-0.1952*x1*y1+0.1334*y1.^2;

If you correct it to

z1=-1.448-0.477*x1-0.4757*y1+0.1473*x1.^2-0.1952*x1.*y1+0.1334*y1.^2;

The two codes give the same results