Hi, I am implementing a nonlinear equation with time in second derivative. The weak form has a form like the following (phi is the test function).
....... .. φ.Un-1.Un - φ. Un-2.Un-1 The solution of U has to be stored for two previous steps but not sure how to form the local_matrix. I don't think a local matrix can be formed for this case (with three phi terms) without simplifying the equation or do a variable conversion to change the second order time to first order as in tutorial 23. Is that right ? Thanks ! Arun.
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