2018-03-07 13:45:11 +0100 received badge ● Student (source) 2018-03-07 08:19:23 +0100 asked a question Integrate expression involving a formal function I am trying to integrate expressions involving a formal function $f(x)$: sage: var('x') sage: function('f')  It works in some simple cases: sage: integrate(cos(f(x)) * f(x).diff(), x) sin(f(x))  However, a slightly more complicated expression is left unchanged: sage: integrate(x * f(x).diff() + f(x), x) integrate(x*diff(f(x), x) + f(x), x)  instead of simplifying to $x\ f(x)$. Is it possible to integrate such expressions in Sage? I tried to use other algorithms (e.g. algorithm='mathematica_free'), but I got this traceback: .local/opt/sage-8.0/local/lib/python2.7/site-packages/sage/symbolic/expression_conversions.pyc in derivative(self, ex, operator) 588 from sage.symbolic.ring import is_SymbolicVariable 589 if self.name_init != "_maxima_init_": --> 590 raise NotImplementedError 591 args = ex.operands() 592 if (not all(is_SymbolicVariable(v) for v in args) or  so it looks like only Maxima algorithm can be used because the derivative operation cannot be converted to anything else.