n = 
Data type symfun (code problem)
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the content of the task:
Follow these steps to obtain expressions for the critical values of f(x)=x^(3/5)*(4-x)^(1/3):
- Define the symbolic function f(x) corresponding to the above formula.
- Use the diff function to differentiate f(x) and define the symbolic function df(x).
- Use the numden function to obtain symbolic expressions for the numerator and denominator of df(x) and store them in the variables n and d, respectively.
- Use the solve function to solve the equations n(x)=0 and d(x)=0. Assign them to the nzeros and zeroros variables respectively.
I have a problem, for this task:
Use the solve function to solve the equations n(x) = 0 and d(x)=0.
Here is my code:
syms x
f(x) = x^(3/5) * (4 - x)^(1/3);
df(x) = diff(f(x));
[n d] = numden(df(x));
nzeros = solve(n == 0);
dzeros = solve(d == 0);
%%%%%%% Kod rysujący jest poniżej %%%%%%%%
figure; hold on; grid on;
fplot(f(x),'LineWidth',2);
fplot(df(x),'LineWidth',2);
ylim([-6,6]);
legend('$f(x)$','$f''(x)$','Interpreter','latex','FontSize',14);
Assign them to the "nzeros" and "dzeros" I can't write lines 5 and lines 6 of the code correctly
Code error:
Variable n must be of data type symfun. It is currently of type sym. Check where the variable is assigned a value.
I tried replacing the code like this:
syms x
f(x) = x^(3/5) * (4 - x)^(1/3);
df(x) = diff(f(x));
[n d] = numden(df(x));
nzeros = solve(symfun(n,x) == 0);
dzeros = solve(symfun(d,x) == 0);
%%%%%%% Kod rysujący jest poniżej %%%%%%%%
figure; hold on; grid on;
fplot(f(x),'LineWidth',2);
fplot(df(x),'LineWidth',2);
ylim([-6,6]);
legend('$f(x)$','$f''(x)$','Interpreter','latex','FontSize',14);
However, the same error message keeps popping up.
Can anyone help?
回答（2 个）
Torsten
2024-5-22
If your MATLAB release throws an error (R2024a does not as you can see above), try
[n(x) d(x)] = numden(df(x))
instead of
[n d] = numden(df(x))
Hi Patryk,
Works o.k. here. What version of Matlab are you using?
syms x
f(x) = x^(3/5) * (4 - x)^(1/3);
df(x) = diff(f(x));
[n d] = numden(df(x))
nzeros = solve(n == 0)
dzeros = solve(d == 0)
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