“Add” object has no attribute “sinh” error in numerical and symbolic expression?

Question

Ultimately, my goal is to numerically differentiate the expression \'u\' (see code) with respect to t, with respect to X and three times with respect to X.

First ide

Answer 1

u is sympy expression. U in python/numpy. The sp.sinh etc are translated to np.sinh etc.

U(Y) evaluates this with the numpy array, but t is still a symbol. That produces a numpy object dtype array, with some sort of mix of numbers and symbols. np.sinh(x) is evaluated as [z.sinh() for z in x]. Since most objects, including symbols don't have a sinh method, this raises your error.

I'm not sure about this, but I suspect you need to lambdify both X and t at once, and evaluate with (Y,T) together, rather than in two steps.

(Later I may try to demonstrate this with a isympy session.)