79 lines
2.2 KiB
Groff
79 lines
2.2 KiB
Groff
.\" $Id: Prob.3,v 1.3 2019/09/09 22:35:37 stolcke Exp $
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.TH Prob 3 "$Date: 2019/09/09 22:35:37 $" SRILM
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.SH NAME
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Prob \- Probabilities for SRILM
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.SH SYNOPSIS
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.nf
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.B "#include <Prob.h>"
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.fi
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.SH DESCRIPTION
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.B Prob
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is a collection of types, constants and utility functions for handling
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probabilities in the SRILM library.
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.SH TYPES
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.TP
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.B Prob
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A floating point number representing a probability.
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.TP
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.B LogP
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Logarithm to base 10 of a probability.
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.SH CONSTANTS
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.TP
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.B LogP_Zero
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Log of probability 0.
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.TP
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.B LogP_Inf
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Log of probability infinity (not a legal probability, of course).
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.TP
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.B LogP_One
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Log of probability 1.
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.TP
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.B LogP_Precision
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The number of significant digits in a LogP
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.TP
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.B Prob_Epsilon
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A positive value close to 0; probability sums less than this should be
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considered effectively zero.
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.SH FUNCTIONS
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.TP
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.B "Boolean parseLogP(const char *\fIstring\fP, LogP &\fIprob\fP)"
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Converts a floating point string representation into a LogP.
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Returns
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.B true
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iff the number was parsed correctly.
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This function should be much faster than generic C library functions
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for floating point parsing.
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Also, it parses singular LogP's (plus/minus infinity) correctly.
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.TP
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.B "Prob LogPtoPPL(LogP \fIprob\fP)"
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Converts a LogP into a perplexity (PPL).
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.TP
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.B "ProbToLogP(Prob \fPprob\fP)"
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Converts a probability into a LogP.
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.TP
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.B "LogP MixLogP(LogP \fIprob1\fP, LogP \fIprob2\fP, double \fIlambda\fP)"
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Computes the LogP resulting from interpolating two LogP's.
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If \fIp1\fP and \fIp2\fP are probabilities corresponding to \fIprob1\fP
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and \fIprob2\fP, respectively, then the result is the LogP corresponding
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to \fIlambda\fP * \fIp1\fP + (1 - \fIlambda\fP) * \fIp2\fP.
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.PP
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The following functions deal with \fIbytelogs\fP.
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Bytelogs are logarithms scaled to represent probabilties and likelihoods
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as a short integer in SRI's DECIPHER(TM) recognizer
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(bytelog(\fIp\fP) = log(\fIp\fP) * 10000.5 / 1024).
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.TP
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.B "double ProbToBytelog(Prob \fIprob\fP)"
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Converts a probability to a bytelog.
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.TP
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.B "double LogPtoBytelog(LogP \fIprob\fP)"
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Convert a LogP to a bytelog.
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.TP
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.B "LogP BytelogToLogP(double \fIbytelog\fP)"
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Convert a bytelog to a LogP.
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.SH "SEE ALSO"
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.SH BUGS
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.SH AUTHOR
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Andreas Stolcke <stolcke@icsi.berkeley.edu>
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.br
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Copyright (c) 1995-1996 SRI International
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