Solve equation for symbolic function

Question

Jonathan Aust 2019-9-9

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/479548-solve-equation-for-symbolic-function

回答： Roshni Garnayak 2019-9-13

I have this simple example:

syms a(t) b(t);
eqn = a(t) * 2 == b(t);
solve(eqn, a(t))

The output is:

Warning: Unable to find explicit solution. For options, see help.
 
ans =
 
Empty sym: 0-by-1

Why is MATLAB not able to solve this? It works if I make a and b constant (not dependent on t), but thats not what I want. The answer I would expect would be something like

a(t) = b(t) * 0.5

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Jonathan Aust 2019-9-9

They are symbolic functions. They do not have a body assigned to them though.

John D'Errico 2019-9-9

Solve apparently does not understand when you ask it to solve for a function.

But there is no reason why you cannot just leave it as a variable, a simple unknown. That it would at some point be dependent on t is something you can deal with later.

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Answer 1

Roshni Garnayak 2019-9-13

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/479548-solve-equation-for-symbolic-function#answer_391673

In this example, the solution doesn’t depend on t. It’s just a representation, so you can use any symbol. Hence, a can be used in place of a(t).

If you have a differential equation where the solution is dependent on t, then you can use the “dsolve” function. Refer to the link below for details on “dsolve” function:

https://www.mathworks.com/help/symbolic/dsolve.html