Hi All,
The euler_lagrange command gives an odd result when the input is a variable that evaluates to an expression
rather than the expression itself. For example:
>> f := x^2*diff(y(x),x)^2 + y^2
x^2*(diff(y(x),x))^2+y^2
>> euler_lagrange(f)
[-x^2*(diff((y(t))(x),x))^2-(y(t))^2=K_0,2*x^2*diff(diff((y(t))(x),x,1),y(t),1)*diff((y(t))(x),x)+2*y(t)=0]
The t isn't an artifact from a previous command, since these were the first two commands of a session, so I don't know what it doing there.
However, using the expression instead of the variable f gives the correct result:
>> euler_lagrange(x^2*diff(y(x),x)^2 + y^2)
diff(y(x),x,2)=((-2*diff(y(x),x)*x+y(x))/x^2)
Jay
Odd result for the euler_lagrange command
Modérateur : xcasadmin