1 Constants and Elementary Functions

▼ |  | Math Library

1 | Constants and Elementary Functions
2 | Flonums
3 | Special Functions
4 | Number Theory
5 | Arbitrary-Precision Floating-Point Numbers (Bigfloats)
6 | Arrays
7 | Matrices and Linear Algebra
8 | Statistics Functions
9 | Probability Distributions
10 | Stuff That Doesn’t Belong Anywhere Else

► | 1 | Constants and Elementary Functions

1.1 | Constants
1.2 | Functions
1.3 | Random Number Generation
1.4 | Measuring Error

On this page:

1.1`` Constants
phi.0
euler.0
gamma.0
catalan.0
1.2`` Functions
float-complex?
number->float-complex
power-of-two?
asinh
acosh
atanh
sum
1.3`` Random Number Generation
random-natural
random-integer
random-bits
1.4`` Measuring Error
absolute-error
relative-error

5.3.6
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### 1`` Constants and Elementary Functions

Neil Toronto <ntoronto@racket-lang.org>

(require math/base)

For convenience, math/base re-exports racket/math as well as providing the values document below.

In general, the functions provided by math/base are elementary functions, or those functions that can be defined in terms of a finite number of arithmetic operations, logarithms, exponentials, trigonometric functions, and constants. For others, see math/special-functions and math/distributions.

#### 1.1`` Constants

If you need more accurate approximations than the following flonums, see, for example, phi.bf and bigfloat->rational.

> value phi.0 : Positive-Flonum

An approximation of φ, the golden ratio.

> > phi.0
> 1.618033988749895

> value euler.0 : Positive-Flonum

An approximation of e, or Euler’s number.

> > euler.0
> 2.718281828459045
> > (exp 1)
> 2.718281828459045

> value gamma.0 : Positive-Flonum

An approximation of γ, the Euler-Mascheroni constant.

> > gamma.0
> 0.5772156649015329

> value catalan.0 : Positive-Flonum

An approximation of G, or Catalan’s constant.

> > catalan.0
> 0.915965594177219

#### 1.2`` Functions

> procedure (float-complex? v) → Boolean
> v : Any

Returns #t when v is of type Float-Complex. Analogous to flonum?.

> procedure (number->float-complex x) → Float-Complex
> x : Number

Returns a new complex number with a flonum real part and a flonum imaginary part. Analogous to real->double-flonum.

> procedure (power-of-two? x) → Boolean
> x : Real

Returns #t when x is an integer power of 2.

Examples:
> > (power-of-two? 1.0)
> #t
> > (power-of-two? 1/2)
> #t
> > (power-of-two? (flnext 2.0))
> #f

> procedure (asinh z) → Number
> z : Number
> procedure (acosh z) → Number
> z : Number
> procedure (atanh z) → Number
> z : Number

The inverses of sinh, cosh, and tanh, which are defined in racket/math (and re-exported by math/base).

> procedure (sum xs) → Real
> xs : (Listof Real)

Like (apply + xs), but incurs rounding error only once when adding inexact numbers. (In fact, the inexact numbers in xs are summed separately using flsum.)

#### 1.3`` Random Number Generation

> procedure (random-natural k) → Natural
> k : Integer

Returns a random natural number less than k, which must be positive. Use (random-natural k) instead of (random k) when k could be larger than 4294967087.

> procedure (random-integer a b) → Integer
> a : Integer
> b : Integer

Returns a random integer n such that (<= a n) and (< n b).

> procedure (random-bits num) → Natural
> num : Integer

Returns a random natural smaller than (expt 2 num); num must be positive. For powers of two, this is faster than using random-natural, which is implemented in terms of random-bits, using biased rejection sampling.

As an example of use, the significands of the numbers returned by bfrandom are chosen by (random-bits (bf-precision)).

#### 1.4`` Measuring Error

> procedure (absolute-error x r) → Real
> x : Real
> r : Real

Usually computes (abs (- x r)) using exact rationals, but handles non-rational reals such as +inf.0 specially.

Examples:
> > (absolute-error 1/2 1/2)
> 0
> > (absolute-error 0.14285714285714285 1/7)
> 7.93016446160826e-18
> > (absolute-error +inf.0 +inf.0)
> 0.0
> > (absolute-error +inf.0 +nan.0)
> +inf.0
> > (absolute-error 1e-20 0.0)
> 1e-20
> > (absolute-error (- 1.0 (fl 4999999/5000000)) 1/5000000)
> 5.751132903242251e-18

> procedure (relative-error x r) → Real
> x : Real
> r : Real

Measures how close an approximation x is to the correct value r, relative to the magnitude of r.

This function usually computes (abs (/ (- x r) r)) using exact rationals, but handles non-rational reals such as +inf.0 specially, as well as r = 0.

Examples:
> > (relative-error 1/2 1/2)
> 0
> > (relative-error 0.14285714285714285 1/7)
> 5.551115123125783e-17
> > (relative-error +inf.0 +inf.0)
> 0.0
> > (relative-error +inf.0 +nan.0)
> +inf.0
> > (relative-error 1e-20 0.0)
> +inf.0
> > (relative-error (- 1.0 (fl 4999999/5000000)) 1/5000000)
> 2.8755664516211255e-11

In the last two examples, relative error is high because the result is near zero. (Compare the same examples with absolute-error.) Because flonums are particularly dense near zero, this makes relative error better than absolute error for measuring the error in a flonum approximation. An even better one is error in ulps; see flulp-error.
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