The E value is computed using the following formula, in which l denotes
the length of the query string, n denotes the number of strings stored
in the database, and S is a score that measures the homology between
nucleic acids or between amino acids. Note that k and m are positive
constants.
E=k*l*n*exp^(－mS)
If the BLAST output results computed using this formula are displayed in
the form 1E-X, this means that the quantity has the value
10-X.