Add tree_size method to symbolic expressions

[slel]

The complexity of a symbolic expression can be measured by the size of its expression tree.

We add a tree_size method to symbolic expressions to count the nodes of the expression tree.

Requested at

• Stack Overflow, 2014, How to obtain leaf count (expression size) in Sage?
• sage-support, 2014, How to obtain leaf count (expression size) in Sage?
• Ask Sage question 57123, 2021, Could we have a leaf_count() function in base sagemath?

In Maple and Mathematica this is called "leaf count", although it counts tree nodes, rather than only leaves.

Other measures of complexity of a symbolic expression:

• length of the expression's string representation
• number of (first-level) operands (see #29738)

CC: @slel

Component: symbolics

Keywords: expression, size, tree

Issue created by migration from https://trac.sagemath.org/ticket/32144

[dkrenn]

comment:2

+1 for adding this