HMM files – transition matrix

[Giorgia M]

I know that each row of an HMM transition matrices must sum up to 1

I get numbers like these: 9.374690e-01 6.253099e-02 or 9.585889e-01 4.141111e-02

Do these numbers sum up to one? How do I read them?

[Simon]

The notation of 9.374690e-01 is called scientific notation, and is a way to display very large or very small values. The “e” stands for exponent and we can read the “eNN” as either

• “times 10 to the power NN”
• “move the decimal point NN places (negative NN means move to the left, positive NN means move to the right”

they both mean the same thing. “e+00” would mean “don’t move the decimal place”. The number before the “e” always has exactly one digit before the decimal point, and that is always non-zero.

Here’s how that works for your numbers:

9.374690e-01 means “take 9.374690 and move the decimal place -01 places” in other words one position to the left. So we have

9.374690e-01 = 0.9374690

6.253099e-02 = 0.06253099

and now we see that indeed 0.9374690 + 0.06253099 = 1

Try for yourself: write these numbers in scientific notation:

 123.435
 0.00043
-3487.12

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 123.435 =  1.23435e+02
 0.00043 =  4.3e-04
-3487.12 = -3.48712e+03

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