2024-06-23

overview of mathematical structures

expressions

expressions represent values and consist of variables, constants, and operators. they do not include an equals sign or assert equality.

  • algebraic expressions:

    • monomial: a single term (eg '5 x')
    • binomial: two terms (eg 'x ** 2 + 2 x')
    • polynomial: multiple terms (eg, '4x ** 3 - 3x ** 2 + 2 x - 1')
  • rational expressions: ratios of polynomials (eg '(x ** 2 - 1) / (x + 1)')
  • exponential expressions: expressions involving exponents (eg '2 ** x')
  • logarithmic expressions: expressions involving logarithms (eg 'log(x)')
  • trigonometric expressions: expressions involving trigonometric functions (eg 'sin(x) + cos(x)')

equations

equations state that two expressions are equal and include an equals sign. they can be solved to find the values of the variables.

  • linear equations: first-degree equations (eg '2 x + 3 = 7')
  • quadratic equations: second-degree equations (eg 'ax ** 2 + bx + c = 0')
  • polynomial equations: higher-degree equations (eg 'x ** 3 - 4x ** 2 + x + 6 = 0')
  • rational equations: equations involving rational expressions (eg '1 / (x + 1) = 2')
  • exponential equations: equations involving exponential expressions (eg '2 ** x = 8')
  • logarithmic equations: equations involving logarithms (eg 'lox(x) = 3')
  • trigonometric equations: equations involving trigonometric functions (eg 'sin(x) = 0.5')
  • differential equations: equations involving derivatives (eg '(d ** 2 * y) / (d x ** 2) + 3 * ((d y) / (d x)) + 2 y = 0')

functions

functions describe a relationship between inputs and outputs. each input corresponds to exactly one output.

  • linear functions: 'f(x) = m x + b'
  • quadratic functions: 'f(x) = a x ** 2 + b x + c'
  • polynomial functions: 'f(x) = x ** 3 - 4 x ** 2 + x + 6'
  • rational functions: ''
  • exponential functions: ''
  • logarithmic functions: ''
  • trigonometric functions: ''
  • piecewise functions

    • defined by different expressions over different intervals
    • ''
  • implicit functions: ''

inequalities

inequalities express a relationship where two expressions are not necessarily equal, but one is greater or less than the other.

  • linear inequalities: '2 x + 3 > 7'
  • polynomial inequalities: ''
  • rational inequalities: ''
  • exponential inequalities: ''
  • logarithmic inequalities: ''
  • trigonometric inequalities: ''

characteristics of functions

arity

the number of arguments or inputs a function takes.

  • types:

    • unary: a function with one input (eg '')

    • binary: a function with two inputs (eg '')

    • n-ary: a function with nn inputs (eg '')

domain

the set of all possible inputs for the function.

example: for 'f(x) = sqrt(x)' the domain is 'x > 0'.

range

the set of all possible outputs of the function.

example: for 'f(x) = x ** 2', the range is 'y > 0'.

codomain

the set of values that could potentially be outputs, not necessarily all of which are achieved.

example: for 'f(real_numbers) -> real_numbers' the codomain is 'real_numbers' even if the range is only non-negative reals.

injectivity (one-to-one)

a function ff is injective if different inputs map to different outputs.

example: ''

surjectivity (onto)

a function ff is surjective if every element in the codomain is mapped by some element in the domain.

example: ''

bijectivity

a function is bijective if it is both injective and surjective.

example: ''

continuity

a function ff is continuous if small changes in the input result in small changes in the output.

example: 'f(x) = x ** 2' is continuous everywhere.

differentiability

a function ff is differentiable if it has a derivative at each point in its domain.

example: 'f(x) = x ** 3' is differentiable everywhere.

periodicity

a function ff is periodic if there exists a positive number tt such that f(x+t)=f(x)f(x+t)=f(x) for all xx.

example: 'f(x) = sin(x)' has a period of '2 pi'.

symmetry

  • even function: 'f(-x) = f(x)' for all 'x' in the domain

    • example: 'f(x) = x ** 2'
  • odd function: 'f(-x) = -f(x)' for all 'x' in the domain

    • example: 'f(x) = x ** 3'

monotonicity

a function is monotonic if it is either entirely non-increasing or non-decreasing.

types:

  • monotonically increasing: ''
  • monotonically decreasing: ''

boundedness

a function ff is bounded if there exists a number mm such that ∣f(x)∣≤m∣f(x)∣≤m for all xx in the domain.

types:

  • bounded above: ''
  • bounded below: ''

inverse function

a function 'f' has an inverse 'f ** -1' if 'f((f ** -1)(y)) = y' and '(f ** -1)(f(x)) = x'

example: the inverse of 'f(x) = 2 x' is '(f ** -1)(x) = x / 2'

plaintext ascii math notation

  • readable plaintext mathematics notation similar to what is used in programming languages

  • avoids symbol proliferation

  • operators, values, and other expressions must be separated by spaces

  • multiplication: *

  • exponentiation: **

  • division: /

  • subtraction: -

  • addition: +

  • application: function_name(argument, ...)

  • definition: function_name(parameter, ...) = ...

  • standard library

    • srqt()

    • expt()

see also