fsurf not drawing cant explain

Question

Xinhua 2019-4-29

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/459111-fsurf-not-drawing-cant-explain

评论： David Wilson 2019-4-30

Try these script below

clear
syms x y z;
f1= 0.594693*x - 0.037385*y - 4.415084e-48*(1.410081e94*x^2 - 1.010367e94*x*y - 7.167399e96*x - 6.594237e94*y^2 + 4.505749e95*y + 8.942503e98)^(1/2) - 26.520424;
f2= 0.594693*x - 0.037385*y + 4.415084e-48*(1.410081e94*x^2 - 1.010367e94*x*y - 7.167399e96*x - 6.594237e94*y^2 + 4.505749e95*y + 8.942503e98)^(1/2) - 26.520424;
fsurf(f1,'FaceColor','red')
hold on
fsurf(f2,'FaceColor','green')
hold off
xlabel('x');
ylabel('y');
zlabel('z');

It produce empty drawing.there are some big numbers in the equation but the final value should be within +-200.No reason it doesn't draw.

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Answer 1

David Wilson 2019-4-29

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/459111-fsurf-not-drawing-cant-explain#answer_372769

编辑：David Wilson 2019-4-29

在 MATLAB Online 中打开

Do you really need to use the symbolic toolbox? Why not just plot a numerical surface? But you are right, your numbers are widely varying and your surfaces are fairly flat.

Below I just took arbitrary ranges.

clear
f1= @(x,y) 0.594693*x - 0.037385*y - 4.415084e-48*(1.410081e94*x.^2 - 1.010367e94*x.*y - 7.167399e96*x - ...
           6.594237e94*y.^2 + 4.505749e95*y + 8.942503e98).^(1/2) - 26.520424;
       
       
f2= @(x,y) 0.594693*x - 0.037385*y + 4.415084e-48*(1.410081e94*x.^2 - 1.010367e94*x.*y - 7.167399e96*x - ...
           6.594237e94*y.^2 + 4.505749e95*y + 8.942503e98).^(1/2) - 26.520424;
xv = linspace(-2,2,20)'; yv = linspace(-3,5,30)';        
[X,Y] = meshgrid(xv,yv)       
F1 = f1(X,Y); 
F2 = f2(X,Y); 
surf(xv, yv, F1) 
hold on
surf(xv, yv, F2) 
hold off 

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Xinhua 2019-4-30

the problem is if I took the range too wide it will produce complex number and it will not draw either and I cant manuelly calculate ranges for every graph I draw.A corret image should produce a cone shape.

David Wilson 2019-4-30

在 MATLAB Online 中打开

One ugly solution is to identify where the complex regions are and then "NaN" them.

It's not overly pretty this way, but can be made better with a finer grid. You could always try fimplicit3 if not satisfied.

clear
f1= @(x,y) 0.594693*x - 0.037385*y - 4.415084e-48*(1.410081e94*x.^2 - 1.010367e94*x.*y - 7.167399e96*x - ...
           6.594237e94*y.^2 + 4.505749e95*y + 8.942503e98).^(1/2) - 26.520424;
       
       
f2= @(x,y) 0.594693*x - 0.037385*y + 4.415084e-48*(1.410081e94*x.^2 - 1.010367e94*x.*y - 7.167399e96*x - ...
           6.594237e94*y.^2 + 4.505749e95*y + 8.942503e98).^(1/2) - 26.520424;
       
% Now use a wide range        
yv = linspace(-300,400,150)'; 
xv = linspace(-300,-120,130)';        
[X,Y] = meshgrid(xv,yv)       
F1 = f1(X,Y); 
F2 = f2(X,Y); 
F1(find(imag(F1)~=0)) = NaN;  % drop complex parts
F2(find(imag(F2)~=0)) = NaN;
%
surf(xv, yv, real(F1)) 
hold on
surf(xv, yv, real(F2)) 
hold off 
shading interp
lighting phong
camlight left