MATLAB: How to solving equation with trials

equationsolvetrials

hi all, i'm a student and i've a assingment and i'm kind a new with matlab.

i have an equation with 2 variables, its like r=(x,T)

i want x and y values to make r=0 and then i will plot a graph to T to x. in more specificly its a rate equation for ammonia synthesis and i'm trying to plot a conversion vs temperature graph.

i try solve with solve(r,T). with this command , i think my equation is kind a complicated and matlab gives an warning; "Warning: Explicit solution could not be found. "

so i'm trying to solve with trials, i want T changes in a to b, and x changes in c to d and which values gives r=0 (10^-3 will be enough to accept 0) display to me this x and T values or even plot a graph.

i know i should use 2 'for loop' like

for T=a:1:b and for x=c:0.01:d

but i dont know how to arrange to r=0 (or 0<=r<=10^-3) and display x,y for r=0.

Best Answer

The fminsearch function might work, but assuming T is temperature and you want to solve for different values of x at defined values of T that make r=0, I suggest fzero. You did not post your function so I cannot run code and test it. (I do not know what r returns as output, or how it works.)

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There appears to be a factor of ‘y(1)’ missing in the last 3 terms of the ‘dy(3)’ equation. (I gave your differential equation as posted to the odeToVectorField function to be certain.)

Also, the if block is not necessary. It does nothing, and produces slower code.

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Try your code with these changes:

    [V1,Sbs] = odeToVectorField(ODE1,ODE2); 
    F1 = matlabFunction(V1,'vars',{'t','Y'});
    cond1 = T(0) == T_inK;
    cond2 = X(0) == 0;
    conds = [cond1; cond2];
    Lspan = [0, 30];
    y0 = [T_inK, 0];
    [t,ys] = ode45(F1, Lspan, y0);
    disp('ODEs Solved');
    
figure
yyaxis left
plot(t,ys(:,1))
yyaxis right
plot(t, ys(:,2))
legend(string(Sbs), 'Location','E')
grid

The code prior to that is unchanged. The first argument to ‘F1’ must be the independent variable vector, even if you don’t use it. Since the only variable in ‘F1’ is ‘Y’ otherwise (as the default dependent variable), that’s all matlabFunction needs to know.

Best Answer

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