What is the difference between weak from Ritz method and variational form Ritz method while solving a boundary value problem ? Can all differential equations take variational form ?
I suggest you follow a similar query thread here : https://www.researchgate.net/post/What-is-the-difference-between-Weighted-residual-methods-and-Variational-or-Weak-methods
See also, https://vtechworks.lib.vt.edu/bitstream/handle/10919/28489/Chapter3FiniteElementMethod.pdf?sequence=14&isAllowed=y