This gem can be used to safely evaluate simple latex expressions.

For example, if you want to evaluate \frac{\xi}{2}+3 where \xi = 3 you can do

LatexEval.eval('\frac{\xi}{2}+3', {xi: 3})

However, if you are going to be evaluating the expression many times, it is best to save the postfix notation first.

postfix = LatexEval.postfix_notation('\frac{\xi}{2}+3')
LatexEval::PostfixNotation.eval(postfix, {xi: 3})

This gem is made up of 3 classes. Latex, Equation, and PostfixNotation. I will explain their uses.

The latex class is used to convert your latex into an equation. For example,

LatexEval::Latex.new('\frac{\xi}{2}+3').equation

will output ((xi)/(2)+3).

Currently, the equation method for the Latex class supports the following latex expressions:

• capital and lowercase Greek letters (\alpha, \Beta, etc.)
• single letter variables (a, b, ..., z)
• fractions in the form of \frac{}{} and \dfrac{}{}
• roots in the form \sqrt{} and \sqrt[]{}
• binary operators
  • multiplication (*, \cdot, \times)
  • division(/)
  • powers (^)
  • modulus (%)
  • addition (+)
  • subtraction (-)
• unary operators
  • positive (+)
  • negative (-)

The equation class is used to convert your equations into postfix notation. For example,

LatexEval::Equation.new('((xi)/(2)+3)').postfix_notation

will output [3, :xi, 2, :divide, :add].

Currently, the postfix_notation method for the Equation class can interpret:

• brackets
• binary operators
  • multiplication (*)
  • division(/)
  • powers (^)
  • modulus (%)
  • addition (+)
  • subtraction (-)
• unary operators
  • positive (+)
  • negative (-)

and will adhere to the generally accepted order of operations.

The postfix equation class is used to safely evaluate postfix notation. For example,

LatexEval::PostfixNotation.new([3, :xi, 2, :divide, :add]).eval({xi: 3})

will output 4.5.

The eval method accepts one argument, which is a hash of variable values.

Currently, the eval method for the PostfixNotation class can interpret:

• binary operators
  • :multiply
  • :divide
  • :power
  • :mod
  • :add
  • :subtract
• unary operators
  • :positive
  • :negative