Scientific notation

From Wikipedia, the free encyclopedia - View original article

 
Jump to: navigation, search

Scientific notation (commonly referred to as "standard form" or "standard index form") is a way of writing numbers that are too big or too small to be conveniently written in decimal form. Scientific notation has a number of useful properties and is commonly used in calculators and by scientists, mathematicians and engineers.

Standard decimal notationNormalized scientific notation
22×100
3003×102
4,321.7684.321768×103
−53,000−5.3×104
6,720,000,0006.72×109
0.22×10−1
0.000 000 007 517.51×10−9

In scientific notation all numbers are written in the form of

a \times 10^b

(a times ten raised to the power of b), where the exponent b is an integer, and the coefficient a is any real number (however, see normalized notation below), called the significand or mantissa. The term "mantissa" may cause confusion, however, because it can also refer to the fractional part of the common logarithm. If the number is negative then a minus sign precedes a (as in ordinary decimal notation).

Decimal floating point is a computer arithmetic system closely related to scientific notation.

Normalized notation[edit]

Any given number can be written in the form a×10^b in many ways: for example, 350 can be written as 3.5×102 or 35×101 or 350×100.

In normalized scientific notation, the exponent b is chosen so that the absolute value of a remains at least one but less than ten (1 ≤ |a| < 10). Thus 350 is written as 3.5×102. This form allows easy comparison of numbers, as the exponent b gives the number's order of magnitude. In normalized notation, the exponent b is negative for a number with absolute value between 0 and 1 (e.g. 0.5 is written as 5×10−1). The 10 and exponent are often omitted when the exponent is 0.

Normalized scientific form is the typical form of expression of large numbers in many fields, unless an unnormalised form, such as engineering notation, is desired. Normalized scientific notation is often called exponential notation—although the latter term is more general and also applies when a is not restricted to the range 1 to 10 (as in engineering notation for instance) and to bases other than 10 (as in 3.15× 2^20).

Engineering notation[edit]

Engineering notation differs from normalized scientific notation in that the exponent b is restricted to multiples of 3. Consequently, the absolute value of a is in the range 1 ≤ |a| < 1000, rather than 1 ≤ |a| < 10. Though similar in concept, engineering notation is rarely called scientific notation. Enginering notation allows the numbers to explicitly match their corresponding SI prefixes, which facilitates reading and oral communication. For example, 12.5×10−9 m can be read as "twelve-point-five nanometers" or written as 12.5 nm, while its scientific notation equivalent 1.25×10−8 m would likely be read out as "one-point-two-five times ten-to-the-negative-eight meters".

Significant figures[edit]

A significant figure is a digit in a number that adds to its precision. This includes all nonzero numbers, zeroes between significant digits, and zeroes indicated to be significant. Leading and trailing zeroes are not significant because they exist only to show the scale of the number. Therefore, 1,230,400 usually has five significant figures—1, 2, 3, 0, and 4; the two zeroes serve only as placeholders and add no precision to the original number.

When a number is converted into normalized scientific notation, it is scaled down to a number between 1 and 10. All of the significant digits remain, but the place holding zeroes are no longer required. Thus 1,230,400 would become 1.2304 x 106. However there is also the possibility that the number may be known to six or more significant figures, in which case the number would be shown as (for instance) 1.23040 x 106. Thus an additional advantage of scientific notation is that the number of significant figures is clearer.

Estimated final digit(s)[edit]

It is customary in scientific measurements to record all the definitely known digits from the measurements, and to estimate at least one additional digit if there is any information at all available to enable the observer to make an estimate. The resulting number contains more information than it would without that extra digit(s), and it (or they) may be considered a significant digit because it conveys some information leading to greater precision in measurements and in aggregations of measurements (adding them or multiplying them together).

Additional information about precision can be conveyed through additional notations. It is often useful to know how exact the final digit(s) are. For instance, the accepted value of the unit of elementary charge can properly be expressed as 1.602176487(40)×10−19 C,[1] which is shorthand for (1.602176487±0.000000040)×10−19 C

E notation[edit]

A calculator display showing the Avogadro constant in E notation

Most calculators and many computer programs present very large and very small results in scientific notation. Because superscripted exponents like 107 cannot always be conveniently displayed, the letter E or e is often used to represent times ten raised to the power of (which would be written as "× 10b") and is followed by the value of the exponent; in other words, for any two real numbers a and b, the usage of "aE+b" would indicate a value of a × 10b. Note that in this usage the character e is not related to the mathematical constant e or the exponential function ex (a confusion that is less likely with capital E); and though it stands for exponent, the notation is usually referred to as (scientific) E notation or (scientific) e notation, rather than (scientific) exponential notation (though the latter also occurs). The use of this notation is not encouraged in publications.[2]

Examples and other notations[edit]

Order of magnitude[edit]

Scientific notation also enables simpler order-of-magnitude comparisons. A proton's mass is 0.0000000000000000000000000016726 kg. If written as 1.6726×10−27 kg, it is easier to compare this mass with that of an electron, given below. The order of magnitude of the ratio of the masses can be obtained by comparing the exponents instead of the more error-prone task of counting the leading zeros. In this case, −27 is larger than −31 and therefore the proton is roughly four orders of magnitude (10000 times) more massive than the electron.

Scientific notation also avoids misunderstandings due to regional differences in certain quantifiers, such as billion, which might indicate either 109 or 1012.

In physics and astrophysics, the number of orders of magnitude between two numbers is sometimes referred to as "dex", a contraction of "decimal exponent". So. for instance if two numbers are within 1 dex of each other, then the ratio of the larger to the smaller number is less than 10. Fractional values can be used so if within 0.5 dex, the ratio is less than \scriptstyle \sqrt{10}, and so on.[8]

Use of spaces[edit]

In normalized scientific notation, in E notation, and in engineering notation, the space (which in typesetting may be represented by a normal width space or a thin space) that is allowed only before and after "×" or in front of "E" or "e" is sometimes omitted, though it is less common to do so before the alphabetical character.[9]

Further examples of scientific notation[edit]

Converting numbers[edit]

Converting a number in these cases means to either convert the number into scientific notation form, convert it back into decimal form or to change the exponent part of the equation. None of these alter the actual number, only how it's expressed.

Decimal to scientific[edit]

First, move the decimal separator point the required amount, n, to make the number's value within a desired range, between 1 and 10 for normalized notation. If the decimal was moved to the left, append x 10n; to the right, x 10-n. To represent the number 1,230,400 in normalized scientific notation, the decimal separator would be moved 6 digits to the left and x 106 appended, resulting in 1.2304×106. The number -0.004 0321 would have its decimal separator shifted 3 digits to the right instead of the left and yield −4.0321×10−3 as a result.

Scientific to decimal[edit]

Converting a number from scientific notation to decimal notation, first remove the x 10n on the end, then shift the decimal separator n digits to the right (positive n) or left (negative n). The number 1.2304×106 would have its decimal separator shifted 6 digits to the right and become 1 230 400, while −4.0321×10−3 would have its decimal separator moved 3 digits to the left and be -0.0040321.

Exponential[edit]

Conversion between different scientific notation representations of the same number with different exponential values is achieved by performing opposite operations of multiplication or division by a power of ten on the significand and an subtraction or addition of one on the exponent part. The decimal separator in the significand is shifted x places to the left (or right) and 1x is added to (subtracted from) the exponent, as shown below.

1.234×103 = 12.34×102 = 123.4×101 = 1234

Basic operations[edit]

Given two numbers in scientific notation,

x_0=a_0\times10^{b_0}

and

x_1=a_1\times10^{b_1}

Multiplication and division are performed using the rules for operation with exponentiation:

x_0 x_1=a_0 a_1\times10^{b_0+b_1}

and

\frac{x_0}{x_1}=\frac{a_0}{a_1}\times10^{b_0-b_1}

Some examples are:

5.67\times10^{-5} \times 2.34\times10^2 \approx 13.3\times10^{-3} = 1.33\times10^{-2}

and

\frac{2.34\times10^2}{5.67\times10^{-5}}  \approx 0.413\times10^{7} = 4.13\times10^6

Addition and subtraction require the numbers to be represented using the same exponential part, so that the significand can be simply added or subtracted. :x_1 = c \times10^{b_0}

Next, add or subtract the significands:

x_0 \pm x_1=(a_0\pm c)\times10^{b_0}

An example:

2.34\times10^{-5} + 5.67\times10^{-6} = 2.34\times10^{-5} + 0.567\times10^{-5} \approx 2.907\times10^{-5}

Other bases[edit]

While base 10 is normally used for scientific notation, powers of other bases can be used too, base 2 being the next most commonly used one.

For example, in base-2 scientific notation, the number 1001 in binary (=9) is written as:

1.001×1011 using binary numbers, or, in E notation,
1.001 E11 (with the letter E now standing for times two to the power), or
1.125 × 23 (using decimal representation).

This is closely related to the base-2 floating-point representation commonly used in computer arithmetic.

Engineering notation can be viewed as base-1000 scientific notation.

See also[edit]

Notes and references[edit]

  1. ^ "NIST value for the elementary charge". Physics.nist.gov. Retrieved 2012-03-06. 
  2. ^ Edwards, John (2009), Submission Guidelines for Authors: HPS 2010 Midyear Proceedings (PDF), McLean, Virginia: Health Physics Society, p. 5, retrieved 2013-03-30 
  3. ^ "Primitive Data Types (The Java Tutorials > Learning the Java Language > Language Basics)". Download.oracle.com. Retrieved 2012-03-06. 
  4. ^ "UH Mānoa Mathematics » Fortran lesson 3: Format, Write, etc". Math.hawaii.edu. 2012-02-12. Retrieved 2012-03-06. 
  5. ^ Report on the Algorithmic Language ALGOL 60, Ed. P. Naur, Copenhagen 1960
  6. ^ "Revised Report on the Algorithmic Language Algol 68". September 1973. Retrieved April 30, 2007. 
  7. ^ "SIMULA Standard As defined by the SIMULA Standards Group - 3.1 Numbers". August 1986. Retrieved October 6, 2009. 
  8. ^ definition of dex in wiktionary.org
  9. ^ Samples of usage of terminology and variants: [1], [2], [3], [4], [5], [6]

External links[edit]