Using For loop to plot graphs of functions

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HUST Student 2018-6-10

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https://ww2.mathworks.cn/matlabcentral/answers/404925-using-for-loop-to-plot-graphs-of-functions

评论： Stephen23 2018-6-10

I'm trying to write a matlab (for loop) code to produce the graphs: Q as a function of A, F as a function of A, Z as a function of A from the known functions f1, f2 and f3 Z = f1 (A, F, Q) F = f2 (A, Q, Z) A = f3 (Z, Q). I made several attempts that were unsuccessful:

clear
syms w e d n A Z F Q;
w=pi;
e=0.5;
d=10;
n=1;
eqn1 = Z+A.*w./(1-Q.*(1+e))*cos(F)==0;
eqn2 = cos(F+2.*Q.*n.*pi)+Z.*((e-Q.*(1+e))./A.*w)==0;
eqn3 = A-1/(2.*w.*abs(sin(Q.*n.*pi))).*(((1-e).*Z).^2+(d.*w+2.*(1+e).*(1-Q).*Q.*n.*pi.*Z).^2).^0.5==0;
equations = [eqn1 eqn2 eqn3];
vars = [A Z F Q];
range = [0 10;-40 40;0 6;NaN NaN];
for A=0:0.5:10;
    for i=1:5
    temp=vpasolve(equations, vars, range, 'random', true);
    sol(i,1)=temp.Z;
    sol(i,2)=temp.F;
    sol(i,3)=temp.Q;
    end
figure (1);
subplot(2,2,1)
plot(A,sol(i,1));
xlabel('A');
ylabel('Z');
subplot(2,2,2)
plot(A,sol(i,2));
xlabel('A');
ylabel('F');
subplot(2,2,3)
plot(A,sol(i,2));
xlabel('A');
ylabel('Q');
end

Error using getEqnsVars (line 50) Expecting two arguments: a vector of equations and a vector of variables.

Error in sym/vpasolve (line 95) [eqns,vars] = getEqnsVars(varargin{1:N});

Error in Sucesso (line 15) temp=vpasolve(equations, vars, range, 'random', true);

I do not know how to solve this error, because in the three equations eqn1 eqn2 eqn3 A is a variable that in the loop assumes the constant values in the interval (0, 10) so in each loop step a system of three equations with three variables (Z, Q, F) supposed to be solved.

If someone can help me I would thank you a lot.