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

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Hi, I using follow code to generate a surface, got fig 1
=========================================================
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;
=========================================================
fig 1
and I change x and y vector step from 0.01 to 0.1, got fig 2
=========================================================
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....

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Accepted Answer

Théophane Dimier
Théophane Dimier on 26 Nov 2020
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

  1 Comment

MacGyver Pan
MacGyver Pan on 27 Nov 2020
it's work.
I read many similar examples, not to point this operation problem.
Thanks very much.

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More Answers (1)

Stephan
Stephan on 26 Nov 2020
Edited: Stephan on 26 Nov 2020
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');

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