fixed points in the plots

Question

hasan s 2021-4-11

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/799267-fixed-points-in-the-plots

评论： hasan s 2021-4-18

采纳的回答： Walter Roberson

POINTS.m

在 MATLAB Online 中打开

Hi,

I have a program that includes a graph of functions in 3D

I need to fix points on the drawing (show the location of the points on the drawing),

I used

hold on ;
plot (A(1),B(2.1),G(3.021),'r*')
plot (A(0.0001),B(3),G(3.21),'r*')
plot (A(3.654),B(3.1),G(2.15),'r*')

But an error appeared to me...

Error in POINTS (line 45)

plot (A(1),B(2.1),G(3.021),'r*')

if any Prof. can help me ...thanks alot

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Answer 1

Walter Roberson 2021-4-11

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/799267-fixed-points-in-the-plots#answer_672832

在 MATLAB Online 中打开

syms A B G

A, B, and G are created as scalar symbols

f = matlabFunction(sum1m2, 'vars', [A, B, G]);  
g = matlabFunction(sum3m4, 'vars', [A, B, G]);  
h = matlabFunction(sum5m6, 'vars', [A, B, G]);  

f, g, and h are created as numeric functions of three inputs.

plot (A(1),B(2.1),G(3.021),'r*')
plot (A(0.0001),B(3),G(3.21),'r*')
plot (A(3.654),B(3.1),G(2.15),'r*')

You try to index scalar A at 1, which works, giving you back the scalar symbol A .

You try to index scalar B at 2.1, which fails, because you cannot index at non-integers... and if you could do that, you would be indexing past the end of the scalar.

You try to index scalar G at 3.021, which fails, non integer, past the end of the scalar. Is it possible that function g was intended? But function g needs three parameters, not one.

I suspect what you want is

plot ((1),(2.1),(3.021),'r*')
plot ((0.0001),(3),(3.21),'r*')
plot ((3.654),(3.1),(2.15),'r*')

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Walter Roberson 2021-4-17

在 MATLAB Online 中打开

NumPoints = 50;
tic
digits(16);
syms A B G
N = 100;
Q1 = rand(10,N);
Q = vpa(reshape(Q1,1,[])); 
sum1=0;sum2=0;sum3=0;sum4=0;sum5=0;sum6=0;
for j=1:1000
    sum1=sum1+1/(A+(G*B*((Q(j))^(G-1))));
    sum2=sum2+(Q(j));
    sum3=sum3+(G*((Q(j))^(G-1)))/(A+(G*B*((Q(j))^(G-1))));
    sum4=sum4+(Q(j))^(G);
    sum5=sum5+(((G*log(Q(j)))*((Q(j))^(G-1)))+((Q(j))^(G-1)))/(A+(B*G*((Q(j))^(G-1))));
    sum6=sum6+((Q(j))^(G))*log(Q(j));
    
end
sum1m2 = vpa(sum1 - sum2);
sum3m4 = vpa(sum3 - sum4);
sum5m6 = vpa(B*sum5-B*sum6);
f = matlabFunction(sum1m2, 'vars', [A, B, G]);  
g = matlabFunction(sum3m4, 'vars', [A, B, G]);  
h = matlabFunction(sum5m6, 'vars', [A, B, G]);  
[Ag, Bg, Gg] = meshgrid(linspace(0, 4,NumPoints));
Fgrid = f(Ag,Bg,Gg);    
Ggrid = g(Ag,Bg,Gg);    
Hgrid = h(Ag,Bg,Gg);    
grids = {Fgrid, Ggrid, Hgrid};
gridnames = {'f', 'g', 'h'};
ngrid = length(grids);
cmap = parula(ngrid);
view(3);
patches = gobjects(1,ngrid);
surfaces = cell(ngrid, 1);
for K = 1 : ngrid
  surfaces{K} = isosurface(Ag, Bg, Gg, grids{K}, 0);
  patches(K) = patch(surfaces{K}, 'facecolor', cmap(K,:), 'edgecolor','none','FaceAlpha', 0.5, 'displayname', gridnames{K});
end
xlabel('A');
ylabel('B');
zlabel('G');
legend show
hold on ;
plot3((1),(2.1),(3.021),'r*')
plot3((0.0001),(3),(3.21),'r*')
plot3((3.654),(3.1),(2.15),'r*')
hold off
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