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require 'cmath'
module Math
class Expon < Function
attr_reader :y_start, :y_end, :tau
attr_reader :a, :b, :c
#
# +DEFAULT_TAU+: default exponential curvature factor for +expon()+
#
DEFAULT_TAU = 0.01
#
# +Math::Expon.new(ystart, yend, xstart, xend, tau = DEFAULT_TAU)+:
#
# exponential curve `y = e^(a*x + b) + c` where:
#
# `c = yend + tau`
#
# Arguments are:
#
# +ystart+, +yend+: start/end y values required
# +xstart+, +xend+: start/end x values
# +tau+: the curvature factor
#
#:nodoc:
def initialize(ys, ye, xs, xe, tau = DEFAULT_TAU)
@y_start = ys
@y_end = ye
@x_start = xs
@x_end = xe
@tau = tau
setup
end
#:doc:
#
# +y(x)+:
#
# Returns a real value (forcing any complex result to its modulus) for any
# given x
#
#:nodoc:
def y(x)
(CMath::exp(self.a*x + self.b) + self.c).abs # we want a real number result, no complex please
end
def label
"tau: #{self.tau}"
end
class << self
#
# +from_yaml(yaml_hash)+:
#
# creates a Math::Expon class from a yaml file which must have the
# relevant fields:
#
# +x_start+
# +x_end+
# +y_start+
# +y_end+
# +tau+
#
def from_yaml(yh)
args = [yh['y_start'], yh['y_end'], yh['x_start'], yh['x_end'], yh['tau']]
new(*args)
end
end
private
def setup
@c = self.y_end + self.tau
exp_sv = self.y_start - self.c # start value of the exponential
exp_ev = self.y_end - self.c # end value of the exponential
x_length = self.x_end - self.x_start
@a = (CMath::log(exp_ev) - CMath::log(exp_sv)) / x_length;
@b= CMath::log(exp_sv) - (self.a * x_start);
end
end
end
Version data entries
25 entries across 25 versions & 1 rubygems