What is 1e-9?

What is 1e-9?

def compare_floats(a, b, epsilon=1e-9): //判斷浮點數是否相等， 實際是判斷兩數相差是否大於那個極微小的數
    return abs(a - b) < epsilon

result = compare_floats(0.1 + 0.2, 0.3)  //現在返回True，正常工作！

 

 

 

 

Dylan Wood

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M.M.S. in Mathematical Sciences & Computational Science, The Ohio State University (Graduated 2016)Updated 3y

It’s a way to write the number .000000001 in scientific notation, i.e., 1 × 10⁻⁹. The “e” is a more compact way to write “× 10^”.

Or in plain English, the “e” here means “times ten raised to the power of”, so 1e-9 can be read in the same way as 1 × 10⁻⁹, “one times ten raised to the power of negative nine”.

This is alternatively referred to as “E-notation”, and it is mostly used as a way to concisely write numbers in scientific notation, so that they are easier to read in text, or where space is limited, like on a calculator display.

Incidentally, the number 1e-9 corresponds to the scientific prefix nano and what is commonly referred to as the “nanoscale”. For example, a nanometer is one-billionth of a meter, or .000000001 meter or more concisely 1e-9 meter.

These are the sorts of length scales on which the field of nanotechnology works.

Scientific notation and metric affixes

 

Deb Chatigny

• 17 hours ago
 
• Updated

You can enter metric affixes or scientific notation to indicate very large or very small numbers. For scientific notation, you can type either a caret (^) or the letter e followed by a number to indicate an exponent. You can use both positive and negative exponents.

For example, to indicate 0.012, you can enter either of the following expressions:

• 1.2*10^-2
• 1.2e-2

To indicate -440,000, you can enter either of the following expressions:

• -4.4*10^5
• -4.4e5

The following table shows how to enter numbers with metric affixes, with scientific notation, and with e notation.

To enter this number	Use this metric affix	Scientific Notation	Use this E Notation	Other Notation
0.1	1d (deci)	10^-1	1e-1
0.01	1c (centi)	10^-2	1e-2	1% (percent)
0.001	1m (milli)	10^-3	1e-3
0.000001	1u (micro)	10^-6	1e-6
0.000000001	1n (nano)	10^-9	1e-9
0.000000000001	1p (pico)	10^-12	1e-12
1,000	1k (kilo)	10^3	1e3
1,000,000	1M (mega)	10^6	1e6
1,000,000,000	1G (giga)	10^9	1e9
1,000,000,000,000	1T (tera)	10^12	1e12

Note: When you use metric affixes or e notation, make sure you do not include spaces between the number and the metric affix or the e.

For more information, see Entering math expressions in assignments or the calculator or Using constants in math expressions.

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