## simplify

Simplify the scalar part of an expression.

When expressions (or sub-expressions) involve scalars, simplification of such expressions can be
'outsourced' to an external scalar computer algebra system, at present either Sympy or Mathematica.
The `simplify`

algorithm finds all scalar sub-expressions and runs the simplification algorithm
of one of these systems on them.ex:= (\sin{x}**2 + \cos{x}**2) A_{m};

\(\displaystyle{}\left({\left(\sin{x}\right)}^{2}+{\left(\cos{x}\right)}^{2}\right) A_{m}\)

((\sin(x))**2 + (\cos(x))**2) A_{m}

simplify(_);

\(\displaystyle{}A_{m}\)

A_{m}

By default it will use the Sympy backend, but if you have compiled Cadabra on a system which has Mathematica installed,
you can also switch it to use Mathematica instead, by using

kernel(scalar_backend="mathematica")