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Cumulative standard deviation: Difference between revisions
→{{header|Forth}}: Fixed to return the running standard deviation
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=={{header|Forth}}==
<lang forth>: f+! ( x addr -- ) dup f@ f+ f! ;
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: st-sum ( stats -- sum ) float+ f@ ;
: st-sumsq ( stats -- sum*sum ) 2 floats + f@ ;
: st-add ( fnum stats -- )▼
1e dup f+! float+▼
fdup dup f+! float+▼
fdup f* f+! ;▼
: st-mean ( stats -- mean )
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: st-stddev ( stats -- stddev )
st-variance fsqrt ;
▲: st-add ( fnum stats -- )
dup
▲ 1e dup f+! float+
▲ fdup dup f+! float+
This variation is more numerically stable when there are large numbers of samples or large sample ranges.
<lang forth>: st-count ( stats -- n ) f@ ;
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: st-add ( x stats -- )
dup
1e dup f+! \ update count
fdup dup st-mean f- fswap
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float+ dup f+! \ update mean
( delta x )
dup f@ f- f* float+ f+!
st-stddev ;</lang>
Usage example:
<lang forth>create stats 0e f, 0e f, 0e f,
2e stats st-add f. \ 0.
4e stats st-add f. \ 1.
4e stats st-add f. \ 0.942809041582063
4e stats st-add f. \ 0.866025403784439
5e stats st-add f. \ 0.979795897113271
5e stats st-add f. \ 1.
7e stats st-add f. \ 1.39970842444753
9e stats st-add f. \ 2.
</lang>
▲stats st-stddev f. \ 2.</lang>
=={{header|Fortran}}==
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