Unrecognized function or variable 'x'.

Question

Maria 2023-11-16

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2048282-unrecognized-function-or-variable-x

编辑： Maria 2023-11-17

Hello.

I don’t understand why I don’t have x defined after running the code, if initially it says errors. Help me please

function  F=M36(x)
F=[3*x(1)*x(2) - x(1)^2 - x(2)^2 - 5; 
   7*x(1)^2 * x(2)^2 - x(1)^4 - x(2)^4 - 155];
options = optimoptions('fsolve','Display','iter');
[~,~] = fsolve(F,[-4,0],options);
[~,~] = fsolve(F,[0,4],options);
disp('Plotting graphs of the left sides of the system equations:')
x=-5:0.1:5; 
y= (3/2).*x+ sqrt((13/4).*x.^2+5); 
plot(y,x,'b')
hold on
x=-5:0.1:5; 
y = sqrt((x^4 + 155) / (7*x^2 - y^2)); 
plot(y,x,'b')
hold on
grid on
legend('Graphic solution');
end

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Dyuman Joshi 2023-11-16

在 MATLAB Online 中打开

It's not clear to me what you want to do.

However, I have cleaned some things up in the code, check it out -

M36

Norm of First-order Trust-region Iteration Func-count ||f(x)||^2 step optimality radius 0 3 169362 1.05e+05 1 1 6 55891.4 1 2.56e+04 1 2 9 29320.3 1 5.51e+03 1 3 12 24368.2 1 633 1 4 15 24050.7 1 6.04 1 5 18 23882 1 387 1 6 21 2418.33 2.5 6e+03 2.5 7 24 1421.97 5.08058 1.33e+04 6.25 8 27 46.4093 0.628623 1.54e+03 6.25 9 30 0.202455 0.0731741 99.1 6.25 10 33 5.13304e-07 0.00327403 0.158 6.25 11 36 4.6714e-17 9.04034e-06 1.5e-06 6.25 12 39 0 5.10498e-11 0 6.25 Equation solved. fsolve completed because the vector of function values is near zero as measured by the value of the function tolerance, and the problem appears regular as measured by the gradient. Norm of First-order Trust-region Iteration Func-count ||f(x)||^2 step optimality radius 0 3 169362 1.05e+05 1 1 6 55891.4 1 2.56e+04 1 2 9 29320.3 1 5.51e+03 1 3 12 24368.2 1 633 1 4 15 24050.7 1 6.04 1 5 18 23882 1 387 1 6 21 2418.33 2.5 6e+03 2.5 7 24 1421.98 5.08058 1.33e+04 6.25 8 27 46.4089 0.628623 1.54e+03 6.25 9 30 0.202457 0.0731742 99.1 6.25 10 33 5.13306e-07 0.00327404 0.158 6.25 11 36 4.6841e-17 9.04036e-06 1.51e-06 6.25 12 39 3.2438e-27 5.02268e-11 1.25e-11 6.25 Equation solved. fsolve completed because the vector of function values is near zero as measured by the value of the function tolerance, and the problem appears regular as measured by the gradient. Plotting graphs of the left sides of the system equations:

Warning: Imaginary parts of complex X and/or Y arguments ignored.

ans = function_handle with value:

@(x)[3*x(1)*x(2)-x(1)^2-x(2)^2-5;7*x(1)^2*x(2)^2-x(1)^4-x(2)^4-155]

function F = M36

% Correction

% vvvv

F = @(x) [3*x(1)*x(2) - x(1)^2 - x(2)^2 - 5;

7*x(1)^2 * x(2)^2 - x(1)^4 - x(2)^4 - 155];

options = optimoptions('fsolve','Display','iter');

[~,~] = fsolve(F,[-4,0],options);

[~,~] = fsolve(F,[0,4],options);

disp('Plotting graphs of the left sides of the system equations:')

x=-5:0.1:5;

y1 = (3/2).*x+ sqrt((13/4).*x.^2+5);

figure

plot(y1,x,'b')

hold on

%Correction

%vv vv vv vv vv vv

y2 = sqrt((x.^4 + 155) ./ (7*x.^2 - y1.^2));

%Changed the color of the plot to differentiate

plot(y2,x,'r')

hold off

grid on

legend('Graphic solution');

end

Maria 2023-11-16

编辑：Maria 2023-11-17

I want to solve a system of nonlinear equations 3*x(1)*x(2) - x(1)^2 - x(2)^2 = 5;

7*x(1)^2 * x(2)^2 - x(1)^4 - x(2)^4 = 155 create a file - m using the extended function fzero, check the solution using the roots function, and also plot solutions

Walter Roberson 2023-11-16

在 MATLAB Online 中打开

syms x [1 2]

eqns = [3*x(1)*x(2) - x(1)^2 - x(2)^2 == 5;

7*x(1)^2 * x(2)^2 - x(1)^4 - x(2)^4 == 155]

eqns =

sol = solve(eqns)

sol = struct with fields:

x1: [4×1 sym] x2: [4×1 sym]

subs([x1, x2], sol)

ans =

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Answer 1

Walter Roberson 2023-11-16

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2048282-unrecognized-function-or-variable-x#answer_1354227

在 MATLAB Online 中打开

F = @(x)[3*x(1)*x(2) - x(1)^2 - x(2)^2 - 5; 
 7*x(1)^2 * x(2)^2 - x(1)^4 - x(2)^4 - 155];

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