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63 lines
1.3 KiB
Forth
63 lines
1.3 KiB
Forth
\ logistic The Logistic function and its first derivative
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\ logistic = Exp( c + a x ) / (1 + Exp( c + a x ) )
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\ d_logistic = a Exp( c + a x ) / (1 + Exp( c + a x ) )^2
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\ Forth Scientific Library Algorithm #4
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\ This code conforms with ANS requiring:
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\ 1. The Floating-Point word set
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\
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\ (c) Copyright 1994 Everett F. Carter. Permission is granted by the
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\ author to use this software for any application provided this
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\ copyright notice is preserved.
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cr .( Logistic V1.2 17 October 1994 EFC )
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: logistic ( --, f: x a c -- z )
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FROT FROT
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F* F+
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FEXP
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FDUP 1.0e0 F+
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F/
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;
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: d_logistic ( -- , f: x a c -- z )
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FSWAP FROT
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FOVER F* FROT F+
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FEXP
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FDUP 1.0e0 F+ FDUP F*
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F/ F*
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;
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\ Examples % 1.0 % 1.0 % 0.0 logistic f. 0.731059
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\ % 3.2 % 1.5 % 0.2 logistic f. 0.993307
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\ % 3.2 % 1.5 % 0.2 d_logistic f. 0.00997209
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# The Code
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~~~
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:logistic (-,f:xac-z)
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f:rot f:rot
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f:* f:+
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f:E f:swap f:power
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f:dup .1.0e0 f:+
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f:/ ;
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:d_logistic (-,f:xac-z)
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f:swap f:rot
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f:over f:* f:rot f:+
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f:E f:swap f:power
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f:dup .1.0e0 f:+ f:dup f:*
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f:/ f:* ;
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~~~
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# Tests
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```
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.1.0 .1.0 .0.0 logistic f:put nl
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.3.2 .1.5 .0.2 logistic f:put nl
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```
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