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udacity373_code / unit5_16.py

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# ----------------
# User Instructions
#
# Implement twiddle as shown in the previous two videos.
# Your accumulated error should be very small!
#
# Your twiddle function should RETURN the accumulated
# error. Try adjusting the parameters p and dp to make
# this error as small as possible.
#
# Try to get your error below 1.0e-10 with as few iterations
# as possible (too many iterations will cause a timeout).
# No cheating!
# ------------
 
from math import *
import random


# ------------------------------------------------
# 
# this is the robot class
#

class robot:

    # --------
    # init: 
    #    creates robot and initializes location/orientation to 0, 0, 0
    #

    def __init__(self, length = 20.0):
        self.x = 0.0
        self.y = 0.0
        self.orientation = 0.0
        self.length = length
        self.steering_noise = 0.0
        self.distance_noise = 0.0
        self.steering_drift = 0.0

    # --------
    # set: 
    #	sets a robot coordinate
    #

    def set(self, new_x, new_y, new_orientation):

        self.x = float(new_x)
        self.y = float(new_y)
        self.orientation = float(new_orientation) % (2.0 * pi)


    # --------
    # set_noise: 
    #	sets the noise parameters
    #

    def set_noise(self, new_s_noise, new_d_noise):
        # makes it possible to change the noise parameters
        # this is often useful in particle filters
        self.steering_noise = float(new_s_noise)
        self.distance_noise = float(new_d_noise)

    # --------
    # set_steering_drift: 
    #	sets the systematical steering drift parameter
    #

    def set_steering_drift(self, drift):
        self.steering_drift = drift
        
    # --------
    # move: 
    #    steering = front wheel steering angle, limited by max_steering_angle
    #    distance = total distance driven, most be non-negative

    def move(self, steering, distance, 
             tolerance = 0.001, max_steering_angle = pi / 4.0):

        if steering > max_steering_angle:
            steering = max_steering_angle
        if steering < -max_steering_angle:
            steering = -max_steering_angle
        if distance < 0.0:
            distance = 0.0


        # make a new copy
        res = robot()
        res.length         = self.length
        res.steering_noise = self.steering_noise
        res.distance_noise = self.distance_noise
        res.steering_drift = self.steering_drift

        # apply noise
        steering2 = random.gauss(steering, self.steering_noise)
        distance2 = random.gauss(distance, self.distance_noise)

        # apply steering drift
        steering2 += self.steering_drift

        # Execute motion
        turn = tan(steering2) * distance2 / res.length

        if abs(turn) < tolerance:

            # approximate by straight line motion

            res.x = self.x + (distance2 * cos(self.orientation))
            res.y = self.y + (distance2 * sin(self.orientation))
            res.orientation = (self.orientation + turn) % (2.0 * pi)

        else:

            # approximate bicycle model for motion

            radius = distance2 / turn
            cx = self.x - (sin(self.orientation) * radius)
            cy = self.y + (cos(self.orientation) * radius)
            res.orientation = (self.orientation + turn) % (2.0 * pi)
            res.x = cx + (sin(res.orientation) * radius)
            res.y = cy - (cos(res.orientation) * radius)

        return res




    def __repr__(self):
        return '[x=%.5f y=%.5f orient=%.5f]'  % (self.x, self.y, self.orientation)


# ------------------------------------------------------------------------
#
# run - does a single control run.


def run(params, printflag = False):
    myrobot = robot()
    myrobot.set(0.0, 1.0, 0.0)
    speed = 1.0
    err = 0.0
    int_crosstrack_error = 0.0
    N = 100
    # myrobot.set_noise(0.1, 0.0)
    myrobot.set_steering_drift(10.0 / 180.0 * pi) # 10 degree steering error


    crosstrack_error = myrobot.y


    for i in range(N * 2):

        diff_crosstrack_error = myrobot.y - crosstrack_error
        crosstrack_error = myrobot.y
        int_crosstrack_error += crosstrack_error

        steer = - params[0] * crosstrack_error  \
            - params[1] * diff_crosstrack_error \
            - int_crosstrack_error * params[2]
        myrobot = myrobot.move(steer, speed)
        if i >= N:
            err += (crosstrack_error ** 2)
        if printflag:
            print myrobot, steer
    return err / float(N)


def twiddle(tol = 0.2): #Make this tolerance bigger if you are timing out!
############## ADD CODE BELOW ####################
    
    p = [0., 0., 0.]
    dp = [1., 1., 1.]
    best_err = run(p)
    n = 0
    while sum(dp) > tol:
        for i in range(len(p)):
            p[i] += dp[i]
            err = run(p) 

            if err < best_err:
                best_err = err 
                dp[i] *= 1.1
            else:
                #try other direction
                p[i] -= 2.0 * dp[i]
                err = run(p)
                if err < best_err:
                    best_err = err
                    dp[i] *= 1.1
                else:
                    p[i] += dp[i]
                    dp[i] *= 0.9
        n += 1
        print "Twiddle #", n, p, ' -> ', best_err
    print ' '
    return p

params = twiddle()
err = run(params)
print '\nFinal parameters: ', params, '\n -> ', err