# Constant Arithmetic

The `Constant Arithmetic`

rule transforms an expression tree by combining two constant values that are separated by a binary operation like `addition`

or `division`

.

### Transformations¶

#### Two Constants¶

The simplest transform is to evaluate two constants that are siblings.

`(4 * 2) + 3`

=`8 + 3`

#### Sibling Skipping¶

The constant simplify rule has the ability to simplify constants across a sibling when the sibling is a variable chunk and the constants are commutatively connected.

For example `2x * 8`

can be transformed into `16x`

because the constants are connected to each other through a multiplication chain that allows commuting.

We can see this by taking a look at the trees for `2x * 8`

and `2 * 8 * x`

and recalling that the commutative proeprty says `a * b = b * a`

:

Satifying the Commutative Property | |
---|---|

We can see that the tree structure has been flipped, but that multiplication nodes still connect the same variables and constants, so the value of the expression remains unchanged.

#### Alternate Tree Forms¶

Math trees can be represented in a number of different equivalent forms, so mathy supports these unnatural groupings to make this rule applicable to more nodes in the tree.

`5 * (8h * t)`

=`40h * t`

`(7 * 10y^3) * x`

=`70y^3 * x`

`(7q * 10y^3) * x`

=`(70q * y^3) * x`

`792z^4 * 490f * q^3`

=`388080z^4 * f * q^3`

`(u^3 * 36c^6) * 7u^3`

=`u^3 * 252c^6 * u^3`

### Examples¶

Info

All the examples shown below are drawn from the mathy test suite that verifies the expected input/output combinations for rule transformations.

Input | Output | Valid |
---|---|---|

10n * 6 | 60n | ✔ |

10 * 6n * x | 60n * x | ✔ |

5 * (8h * t) | 40h * t | ✔ |

(u^3 * 36c^6) * 7u^3 | u^3 * 252c^6 * u^3 | ✔ |

792z^4 * 490f * q^3 | 388080z^4 * f * q^3 | ✔ |

(7q^6 * 10y^3) * 2q | (70q^6 * y^3) * 2q | ✔ |

(7q * 10y^3) * 2q | (70q * y^3) * 2q | ✔ |

144 * (1o) * s | 144o * s | ✔ |

2y * 5 * (8h * t) + 2x | 2y * 40h * t + 2x | ✔ |

5 * (8h * t) | 40h * t | ✔ |

5 * (8h * t) + 2x | 40h * t + 2x | ✔ |

2 * (2 * x) | 4x | ✔ |

10 + 17 | 27 | ✔ |

2.5 - 1.5 | 1 | ✔ |

7 + 4 | 11 | ✔ |

1 - 2 | -1 | ✔ |

4 / 2 | 2 | ✔ |

5 * 5 | 25 | ✔ |

13f^4 * (5f^4 + 7) | --- | --- |

(7q^6 + 10y^3) * 2q | --- | --- |

2 + 2x | --- | --- |

2x - 2 | --- | --- |

12 * y^2 | --- | --- |

x - 2 | --- | --- |