plot surface using different x,y vector increment and got different graph

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

[Théophane Dimier]

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

[MacGyver Pan]

it's work.

I read many similar examples, not to point this operation problem.

Thanks very much.

Answer 2

[Stephan]

You did not multiply elementwise, also you can shorten your code a little bit:

fun = @(x,y) -1.448-0.477*x-0.4757*y+0.1473*x.^2-0.1952*x.*y+0.1334*y.^2;

xl=0:0.1:1;
yl=0:0.1:1;
[x1,y1]=meshgrid(xl,yl);
z1=fun(x1,y1);
figure
surf(xl,yl,z1,'FaceColor','red','LineStyle','none');

xs=0:0.01:1;
ys=0:0.01:1;
[x2,y2]=meshgrid(xs,ys);
z2=fun(x2,y2);
figure
surf(xs,ys,z2,'FaceColor','red','LineStyle','none');

[MacGyver Pan]

thanks