How can I solve the following derative problem in Matlab ?

[Steven Lord]

This sounds like a homework assignment. If it is, show us the code you've written to try to solve the problem and ask a specific question about where you're having difficulty and we may be able to provide some guidance.

If you aren't sure where to start because you're not familiar with how to write MATLAB code, I suggest you start with the MATLAB Onramp tutorial (https://www.mathworks.com/support/learn-with-matlab-tutorials.html) to quickly learn the essentials of MATLAB.

If you aren't sure where to start because you're not familiar with the mathematics you'll need to solve the problem, I recommend asking your professor and/or teaching assistant for help.

[Vuqar Samedov]

Dear Steven Lord,

I can not write the command correctly in the matlab program. I need help.

syms x t

>> y=(x^3+5*x-4);

>> x=(t^2+t);

>> t=-1;

>> dy_dt = diff(y,t)

Error using sym/diff (line 70)

Second argument must be a variable or a nonnegative integer specifying the number of differentiations.

[Vuqar Samedov]

I am a student. I'm learning a new Matlab program. Friends, please help me solve this problem.

Answer 1

[Bjorn Gustavsson]

When you assign:

t = -1;

t becomes a standard double scalar, and is no longer a symbolic variable. So that's where you go completely wrong. Before that, when you describe your variable/function y it becomes a function of x, after that you assign x to some polynomial in t. That second assignment does not have "time-traveling" powers, it does not retroactively affect the definition for y, think of an assignment as "from here on forward...". Try to change order of your definitions...

HTH

[Vuqar Samedov]

I am a student. I'm learning a new Matlab program. Friends, please help me solve this problem.

Answer 2

[Vuqar Samedov]

[Vuqar Samedov]

How can I solve the following derative problem in Matlab ?

[Bjorn Gustavsson]

You are pretty much on the right track.

1, Define your symbolic variables.

2, Look at the problem at hand, not that y depends on x that in turn, depends on t.

3, try do the assignments to y and x in different order, and see what happens when you run diff(y,x) and diff(y,t).

4, if something get you closer to the solution, have a look at how you can proceed from there.

5, a useful function might be matlabFunction - have a look at the help and documentation for that one.