# integrate_by_parts

Integrate by parts away from the indicated expression

Integrate by parts. This requires an expression with an
object carrying a `Derivative`

property. The algorithm should be given
an expression that any derivatives should be integrated away from. An example
makes this more clear:\partial{#}::PartialDerivative;
ex:= \int{ \partial_{m}{ A } B C D }{x};

\(\displaystyle{}\text{Attached property PartialDerivative to }\partial{\#}.\)

\(\displaystyle{}\int{}\partial_{m}{A} B C D\, {\rm d}x\)

integrate_by_parts(_, $A$);

\(\displaystyle{}-\int{}A \partial_{m}\left(B C D\right)\, {\rm d}x\)

product_rule(_);

\(\displaystyle{}-\int{}A \left(\partial_{m}{B} C D+B \partial_{m}{C} D+B C \partial_{m}{D}\right)\, {\rm d}x\)

distribute(_);

\(\displaystyle{}-\int{}\left(A \partial_{m}{B} C D+A B \partial_{m}{C} D+A B C \partial_{m}{D}\right)\, {\rm d}x\)

Note that

`integrate_by_parts`

only does the formal manipulation of moving the
derivative around. If you want to discard derivatives of objects which are constant,
you need to use the `Depends`

property to indicate on which coordinates or derivatives
objects depend, and the `unwrap`

algorithm to eliminate derivatives of constants,
as in the following lines.{B,D}::Depends(\partial);

\(\displaystyle{}\text{Attached property Depends to }\left(B, \mmlToken{mo}[linebreak="goodbreak"]{} D\right).\)

unwrap(ex);

\(\displaystyle{}-\int{}\left(A \partial_{m}{B} C D+A B C \partial_{m}{D}\right)\, {\rm d}x\)