optimize.py

用python实现的邮件过滤器

#
__version__ = '$Id: optimize.py,v 1.2 2003/01/14 05:38:20 anthonybaxter Exp $'
#
# Optimize any parametric function.
#
import copy
import Numeric

def SimplexMaximize(var, err, func, convcrit = 0.001, minerr = 0.001):
    var = Numeric.array(var)
    simplex = [var]
    for i in range(len(var)):
        var2 = copy.copy(var)
        var2[i] = var[i] + err[i]
        simplex.append(var2)
    value = []
    for i in range(len(simplex)):
        value.append(func(simplex[i]))
    while 1:
        # Determine worst and best
        wi = 0
        bi = 0
        for i in range(len(simplex)):
            if value[wi] > value[i]:
                wi = i
            if value[bi] < value[i]:
                bi = i
        # Test for convergence
        #print "worst, best are",wi,bi,"with",value[wi],value[bi]
        if abs(value[bi] - value[wi]) <= convcrit:
            return simplex[bi]
        # Calculate average of non-worst
        ave=Numeric.zeros(len(var), 'd')
        for i in range(len(simplex)):
            if i != wi:
                ave = ave + simplex[i]
        ave = ave / (len(simplex) - 1)
        worst = Numeric.array(simplex[wi])
        # Check for too-small simplex
        simsize = Numeric.add.reduce(Numeric.absolute(ave - worst))
        if simsize <= minerr:
            #print "Size of simplex too small:",simsize
            return simplex[bi]
        # Invert worst
        new = 2 * ave - simplex[wi]
        newv = func(new)
        if newv <= value[wi]:
            # Even worse. Shrink instead
            #print "Shrunk simplex"
            #print "ave=",repr(ave)
            #print "wi=",repr(worst)
            new = 0.5 * ave + 0.5 * worst
            newv = func(new)
        elif newv > value[bi]:
            # Better than the best. Expand
            new2 = 3 * ave - 2 * worst
            newv2 = func(new2)
            if newv2 > newv:
                # Accept
                #print "Expanded simplex"
                new = new2
                newv = newv2
        simplex[wi] = new
        value[wi] = newv

def DoubleSimplexMaximize(var, err, func, convcrit=0.001, minerr=0.001):
    err = Numeric.array(err)
    var = SimplexMaximize(var, err, func, convcrit*5, minerr*5)
    return SimplexMaximize(var, 0.4 * err, func, convcrit, minerr)