Ergebnis enthält "oder"

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Artur Walter
Artur Walter 2023-11-8
评论： Dyuman Joshi 2023-11-22
Ich erhalte
eqn(x) = y(x) == 0 | y(x)*diff(y(x), x, x) + diff(y(x), x)^2 == 0
Wie kann ich auf zweite Bedingung zugreifen?
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Artur Walter
Artur Walter 2023-11-10
I typed
f = y(x)^2 * (diff(y(x), x))^2
eqn = functionalDerivative(f,y) == 0

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回答（2 个）

Dyuman Joshi
Dyuman Joshi 2023-11-16
Ran in:
syms y(x)
f = y(x)^2 * (diff(y(x), x))^2;
eqn = functionalDerivative(f,y) == 0;
%Get the equation mentioned in the question description by using simplify()
eqn = simplify(eqn)
eqn(x) = 
%Children of the expression
z = children(eqn)
z = 1×2 cell array
{[y(x) == 0]} {[y(x)*diff(y(x), x, x) + diff(y(x), x)^2 == 0]}
%Access the second condition
condition2 = z{2}
condition2 = 
Aiswarya
Aiswarya 2023-11-16
Hallo, ich würde die Frage auf Englisch beantworten.
(Hi,
I would be answering the question in English)
I understand that on equating a differential expression to zero, you obtained a conditional expression as a result.
The result obtained from the 'functionalDerviative' is a symbolic function and there is no direct way to just extract the second part of the "or" expression. However you can access the second condition by assuming condition for 'y' as shown in the following image.
You can use the assume function (https://www.mathworks.com/help/symbolic/sym.assume.html) to set non zero condition for y. And then simplify the equation to obtain just the second condition.

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