“For loop” to plot graphs of functions

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, if anyone can help me I would thank you a lot.

[Jan]

Please post your attempts and explain "unsuccessful" with details, e.g. error messages or differences between the results and your expectations. Then an answer will be easier and more likely match your needs.

[HUST Student]

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. Thank.

[HUST Student]

From the equations eqn1 eqn2 eqn3 I am expecting to get the graphs like these (Q as a function of A, F as a function of A, Z as a function of A)

[HUST Student]

[KALYAN ACHARJYA]

As per of your code the plot having 1 x-axis (A) and 3 y-axes (Z, F, Q), clarify?

Also following two subplots are same-

subplot(2,2,2)
plot(A,sol(i,2));
subplot(2,2,3)
plot(A,sol(i,2));

[Stephen23]

See also:

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

Answer 1

[Anurag Ojha]

Hello

To produce the graphs Q as a function of A, F as a function of A, and Z as a function of A, you can use a for loop in MATLAB. I am adding my code below for your reference, I have taken a simple example to show how it could be done. You can modify it according to your use case.

% Define the known functions
f1 = @(A, F, Q) A + F + Q;
f2 = @(A, Q, Z) A - Q + Z;
f3 = @(Z, Q) Z + Q;

% Define the range of A values
A = 1:0.1:10;

% Initialize arrays to store the results
Q_values = zeros(size(A));
F_values = zeros(size(A));
Z_values = zeros(size(A));

% Compute the values for Q, F, and Z for each A value
for i = 1:length(A)
    Q_values(i) = f1(A(i), F_values(i), Q_values(i));
    F_values(i) = f2(A(i), Q_values(i), Z_values(i));
    Z_values(i) = f3(Z_values(i), Q_values(i));
end

% Plot the graphs
figure;
subplot(3, 1, 1);
plot(A, Q_values);
xlabel('A');
ylabel('Q');
title('Q as a function of A');

subplot(3, 1, 2);
plot(A, F_values);
xlabel('A');
ylabel('F');
title('F as a function of A');

subplot(3, 1, 3);
plot(A, Z_values);
xlabel('A');
ylabel('Z');
title('Z as a function of A');

I hope this helps!