Numbers #

Math.js supports three types of numbers:

Configuration #

Most functions can determine the type of output from the type of input: a number as input will return a number as output, a BigNumber as input returns a BigNumber as output. Functions which cannot determine the type of output from the input (for example math.eval) use the default number type, which can be configured when instantiating math.js:

  number: 'number' // Default type of number: 
                   // 'number' (default), 'BigNumber', or 'Fraction'

Round-off errors #

Math.js uses the built-in JavaScript Number type. A Number is a floating point number with a limited precision of 64 bits, about 16 digits. The largest integer number which can be represented by a JavaScript Number is +/- 9007199254740992 (+/- 2^53). Because of the limited precision of floating point numbers round-off errors can occur during calculations. This can be easily demonstrated:

// a round-off error
0.1 + 0.2;            // 0.30000000000000004
math.add(0.1, 0.2);   // 0.30000000000000004

In most cases, round-off errors don’t matter: they have no significant impact on the results. However, it looks ugly when displaying output to a user. A solution is to limit the precision just below the actual precision of 16 digits in the displayed output:

// prevent round-off errors showing up in output
var ans = math.add(0.1, 0.2);       //  0.30000000000000004
math.format(ans, {precision: 14});  // '0.3'

Alternatives are to use Fractions which store a number as a numerator and denominator, or BigNumbers, which store a number with a higher precision.

Minimum and maximum #

A Number can store values between 5e-324 and 1.7976931348623157e+308. Values smaller than the minimum are stored as 0, and values larger than the maximum are stored as +/- Infinity.

// exceeding the maximum and minimum number
console.log(1e309);   // Infinity
console.log(1e-324);  // 0

Equality #

Because of rounding errors in calculations, it is unsafe to compare JavaScript Numbers. For example executing 0.1 + 0.2 == 0.3 in JavaScript will return false, as the addition 0.1 + 0.2 introduces a round-off error and does not return exactly 0.3.

To solve this problem, the relational functions of math.js check whether the relative difference between the compared values is smaller than the configured option epsilon. In pseudo code (without exceptions for 0, Infinity and NaN):

diff = abs(x - y)
nearlyEqual = (diff <= max(abs(x), abs(y)) * EPSILON) OR (diff < DBL_EPSILON)


Note that the relational functions cannot be used to compare small values (< 2.22e-16). These values are all considered equal to zero.


// compare values having a round-off error
console.log(0.1 + 0.2 == 0.3);            // false
console.log(math.equal(0.1 + 0.2, 0.3));  // true

// small values (< 2.22e-16) cannot be compared
console.log(3e-20 == 3.1e-20);            // false
console.log(math.equal(3e-20, 3.1e-20));  // true

The available relational functions are: compare, equal, larger, largerEq, smaller, smallerEq, unequal.

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