fuz_log.m

FISMAT accommodates different arithmetic operators, fuzzification and defuzzification algorithm, imp

function f = fuz_log(f1)

% f=fuz_log(f1)
%
% (natural) logarithm of a (LR-) fuzzy interval (number).
% f = f1 = [xmin xmax m n alpha beta] s. Definition for LR-sets.
% ymin=0 and ymax=1 as a condition.
%
% f = [xmin, xmax, log(m), log(n), log(m/(m-alpha)), log((n+beta)/n)]
% (log ist auch hier der natuerliche Logarithmus)
%
% FSTB - Fuzzy Systems Toolbox for MATLAB
% Copyright (c) 1993-1996 by Olaf Wolkenhauer
% Control Systems Centre at UMIST
% Manchester M60 1QD, UK
%
% 8-Feb-1994
 
m = f1(3); n = f1(4); alpha = f1(5); beta = f1(6);
if fuz_sign(f1)==3;   % f1 not positive and not negative
  error('Error: (LR-) fuzzy-intervall (number) zero.fuz_log impossible !');
end;
if fuz_sign(f1)==2; 
  error('Error: negative argument !');
end;

f(1) = f1(1);  f(2) = f1(2);              % xmin, xmax
f(3) = log(m); f(4) = log(n);             % m, n
f(5) = log(m/(m-alpha));                  % alpha
f(6) = log((n+beta)/n);                   % beta