Hill climbing. A surface with only one maximum. Hill-climbing techniques are well-suited for optimizing over such surfaces, and will converge to the global maximum. In numerical analysis, hill climbing is a mathematical optimization technique which belongs to the family of local search. It is an iterative algorithm that starts with an arbitrary ...See full list on cs50.harvard.edu Hill climbing. A surface with only one maximum. Hill-climbing techniques are well-suited for optimizing over such surfaces, and will converge to the global maximum. In numerical analysis, hill climbing is a mathematical optimization technique which belongs to the family of local search. It is an iterative algorithm that starts with an arbitrary ...There are several variations of Hill Climbing, including steepest ascent Hill Climbing, first-choice Hill Climbing, and simulated annealing. In steepest ascent Hill Climbing, the algorithm evaluates all the possible moves from the current solution and selects the one that leads to the best improvement.Hill climbing is basically a search technique or informed search technique having different weights based on real numbers assigned to different nodes, branches, and goals in a path. In AI, machine learning, deep learning, and machine vision, the algorithm is the most important subset. With the help of these algorithms, ( What Are Artificial ...Feb 6, 2023 · A node of hill climbing algorithm has two components which are state and value. Hill climbing algorithm is a technique which is used for optimizing the mathematical problems. One of the widely discussed examples of Hill climbing algorithm is Traveling-salesman Problem in which we need to minimize the distance traveled by the salesman. Example 1 Apply the hill climbing algorithm to solve the blocks world problem shown in Figure. Solution To use the hill climbing algorithm we need an evaluation function or a heuristic function.In this video we will talk about local search method and discuss one search algorithm hill climbing which belongs to local search method. We will also discus...Random-restart hill climbing is a series of hill-climbing searches with a randomly selected start node whenever the current search gets stuck. See also simulated annealing -- in a moment. A hill climbing example A hill climbing example (2) A local heuristic function Count +1 for every block that sits on the correct thing.Feb 8, 2022 · Ex:- Some games like chess, hill climbing, certain design and scheduling problems. Figure 5: AI Search Algorithms Classification (Image designed by Author ) Search algorithm evaluating criteria: Simulated Annealing (SA) • SA is a global optimization technique. • SA distinguishes between different local optima. SA is a memory less algorithm, the algorithm does not use any information gathered during the search SA is motivated by an analogy to annealing in solids. Simulated Annealing – an iterative improvement algorithm. 7/23/2013 4.Hill climbing algorithm in artificial intelligence sandeep54552 4.8K views • 7 slides Hill climbing algorithm Dr. C.V. Suresh Babu 2.4K views • 14 slides Heuristic Search Techniques Unit -II.ppt karthikaparthasarath 669 views • 31 slidesIn artificial intelligence and machine learning, the straightforward yet effective optimisation process known as hill climbing is employed. It is a local search algorithm that incrementally alters a solution in one direction, in the direction of the best improvement, in order to improve it. Starting with a first solution, the algorithm assesses ...Apr 20, 2023 · Courses Hill climbing is a simple optimization algorithm used in Artificial Intelligence (AI) to find the best possible solution for a given problem. It belongs to the family of local search algorithms and is often used in optimization problems where the goal is to find the best solution from a set of possible solutions. Hill-Climbing Search The hill-climbing search algorithm (or steepest-ascent) moves from the current state towards the neighbor-ing state that increases the objective value the most. The algorithm does not maintain a search tree but only the states and the corresponding values of the objective. The “greediness" of hill-climbing makes it vulnera- N-Queens Problem. N - Queens problem is to place n - queens in such a manner on an n x n chessboard that no queens attack each other by being in the same row, column or diagonal. It can be seen that for n =1, the problem has a trivial solution, and no solution exists for n =2 and n =3. So first we will consider the 4 queens problem and then ...Breadth First Search Ravi Kumar B N, Asst.Prof,CSE,BMSIT 27. Breadth First Search Algorithm: 1. Create a variable called NODE-LIST and set it to initial state 2. Until a goal state is found or NODE-LIST is empty do a. Remove the first element from NODE-LIST and call it E. If NODE- LIST was empty, quit b.Courses. Artificial Intelligence (AI) refers to the simulation of human intelligence in machines that are programmed to think and act like humans. It involves the development of algorithms and computer programs that can perform tasks that typically require human intelligence such as visual perception, speech recognition, decision-making, and ...Disadvantages: The question that remains on hill climbing search is whether this hill is the highest hill possible. Unfortunately without further extensive exploration, this question cannot be answered. This technique works but as it uses local information that’s why it can be fooled. The algorithm doesn’t maintain a search tree, so the ... hill climbing search algorithm1 hill climbing algorithm evaluate initial state, if its goal state quit, otherwise make current state as initial state2 select...Disadvantages: The question that remains on hill climbing search is whether this hill is the highest hill possible. Unfortunately without further extensive exploration, this question cannot be answered. This technique works but as it uses local information that’s why it can be fooled. The algorithm doesn’t maintain a search tree, so the ... * Simple Hill Climbing Example: coloured blocks Heuristic function: the sum of the number of different colours on each of the four sides (solution = 16). * Steepest-Ascent Hill Climbing (Gradient Search) Considers all the moves from the current state. Selects the best one as the next state. For example, the travelling salesman problem, the eight-queens problem, circuit design, and a variety of other real-world problems. Hill Climbing has been used in inductive learning models. One such example is PALO, a probabilistic hill climbing system which models inductive and speed-up learning.Introduction to Hill Climbing Algorithm. Hill Climbing is a self-discovery and learns algorithm used in artificial intelligence algorithms. Once the model is built, the next task is to evaluate and optimize it. Hill climbing is one of the optimization techniques which is used in artificial intelligence and is used to find local maxima.For example, in the graph below, (J) will go to (K) and vice versa repeatedly. If I was programming it, I guess I would put some sort of flag on the visited states so I know if I'm revisiting the same one. However, there is no mention of this in the documentation (i.e here, here) about the Steepest Hill Climbing algorithm.Techniques of knowledge representation. There are mainly four ways of knowledge representation which are given as follows: Logical Representation. Semantic Network Representation. Frame Representation. Production Rules. 1. Logical Representation. Logical representation is a language with some concrete rules which deals with propositions and has ...Introduction to hill climbing algorithm. A hill-climbing algorithm is a local search algorithm that moves continuously upward (increasing) until the best solution is attained. This algorithm comes to an end when the peak is reached. This algorithm has a node that comprises two parts: state and value.Hill climbing is basically a search technique or informed search technique having different weights based on real numbers assigned to different nodes, branches, and goals in a path. In AI, machine learning, deep learning, and machine vision, the algorithm is the most important subset. With the help of these algorithms, ( What Are Artificial ...Simulated Annealing (SA) • SA is a global optimization technique. • SA distinguishes between different local optima. SA is a memory less algorithm, the algorithm does not use any information gathered during the search SA is motivated by an analogy to annealing in solids. Simulated Annealing – an iterative improvement algorithm. 7/23/2013 4.ICS 171 Fall 2006 Summary Heuristics and Optimal search strategies heuristics hill-climbing algorithms Best-First search A*: optimal search using heuristics Properties of A* admissibility, monotonicity, accuracy and dominance efficiency of A* Branch and Bound Iterative deepening A* Automatic generation of heuristics Problem: finding a Minimum Cost Path Previously we wanted an arbitrary path to ... Artificial Intelligence Methods Graham Kendall Hill Climbing Hill Climbing Hill Climbing - Algorithm 1. Pick a random point in the search space 2. Consider all the neighbours of the current state 3. Choose the neighbour with the best quality and move to that state 4. Repeat 2 thru 4 until all the neighbouring states are of lower quality 5. Best first search algorithm: Step 1: Place the starting node into the OPEN list. Step 2: If the OPEN list is empty, Stop and return failure. Step 3: Remove the node n, from the OPEN list which has the lowest value of h (n), and places it in the CLOSED list. Step 4: Expand the node n, and generate the successors of node n. Breadth First Search Ravi Kumar B N, Asst.Prof,CSE,BMSIT 27. Breadth First Search Algorithm: 1. Create a variable called NODE-LIST and set it to initial state 2. Until a goal state is found or NODE-LIST is empty do a. Remove the first element from NODE-LIST and call it E. If NODE- LIST was empty, quit b.Artificial Intelligence Methods Graham Kendall Hill Climbing Hill Climbing Hill Climbing - Algorithm 1. Pick a random point in the search space 2. Consider all the neighbours of the current state 3. Choose the neighbour with the best quality and move to that state 4. Repeat 2 thru 4 until all the neighbouring states are of lower quality 5.HILL CLIMBING: AN INTRODUCTION • Hill Climbing is a heuristic search used for mathematical optimization problems in the field of Artificial Intelligence. • Given a large set of inputs and a good heuristic function, it tries to find a sufficiently good solution to the problem.For example, in the graph below, (J) will go to (K) and vice versa repeatedly. If I was programming it, I guess I would put some sort of flag on the visited states so I know if I'm revisiting the same one. However, there is no mention of this in the documentation (i.e here, here) about the Steepest Hill Climbing algorithm.Following are the types of hill climbing in artificial intelligence: 1. Simple Hill Climbing. One of the simplest approaches is straightforward hill climbing. It carries out an evaluation by examining each neighbor node's state one at a time, considering the current cost, and announcing its current state.Hill Climbing. Hill climbing is one type of a local search algorithm. In this algorithm, the neighbor states are compared to the current state, and if any of them is better, we change the current node from the current state to that neighbor state.Mar 3, 2022 · Algorithm for Simple Hill Climbing: Step 1: Evaluate the initial state, if it is a goal state then return success and Stop. Step 2: Loop Until a solution is found or there is no new operator left ... Hill-Climbing Search The hill-climbing search algorithm (or steepest-ascent) moves from the current state towards the neighbor-ing state that increases the objective value the most. The algorithm does not maintain a search tree but only the states and the corresponding values of the objective. The “greediness" of hill-climbing makes it vulnera-Simple Hill Climbing: Simple hill climbing is the simplest way to implement a hill climbing algorithm. It only evaluates the neighbor node state at a time and selects the first one which optimizes current cost and set it as a current state.Greedy search example Arad (366) 6 februari Pag. 2008 7 AI 1 Assume that we want to use greedy search to solve the problem of travelling from Arad to Bucharest. The initial state=Arad Greedy search example Arad Sibiu(253) Zerind(374) Pag. 2008 8 AI 1 The first expansion step produces: – Sibiu, Timisoara and Zerind Greedy best-first will ...4. Uniform-cost Search Algorithm: Uniform-cost search is a searching algorithm used for traversing a weighted tree or graph. This algorithm comes into play when a different cost is available for each edge. The primary goal of the uniform-cost search is to find a path to the goal node which has the lowest cumulative cost.Sep 8, 2019 · Algorithm for Simple Hill Climbing: Step 1: Evaluate the initial state, if it is goal state then return success and Stop. Step 2: Loop Until a solution is found or there is no new operator left to ... Simple Hill Climbing: Simple hill climbing is the simplest way to implement a hill climbing algorithm. It only evaluates the neighbor node state at a time and selects the first one which optimizes current cost and set it as a current state.Such a technique is called Means-Ends Analysis. Means-Ends Analysis is problem-solving techniques used in Artificial intelligence for limiting search in AI programs. It is a mixture of Backward and forward search technique. The MEA technique was first introduced in 1961 by Allen Newell, and Herbert A. Simon in their problem-solving computer ...Hill-climbing Search The successor function is where the intelligence lies in hill-climbing search It has to be conservative enough to preserve significant “good” portions of the current solution And liberal enough to allow the state space to be preserved without degenerating into a random walk Hill-climbing search Problem: depending on ...Here we discuss the types of a hill-climbing algorithm in artificial intelligence: 1. Simple Hill Climbing. It is the simplest form of the Hill Climbing Algorithm. It only takes into account the neighboring node for its operation. If the neighboring node is better than the current node then it sets the neighbor node as the current node.This information can be in the form of heuristics, estimates of cost, or other relevant data to prioritize which states to expand and explore. Examples of informed search algorithms include A* search, Best-First search, and Greedy search. Example: Greedy Search and Graph Search. Here are some key features of informed search algorithms in AI:Jan 27, 2018 · The application of the hill- climbing algorithm to a tree that has been generated prior to the search is illustrated in Figure 11.1. State Space Representation and Search Page 17 Figure 11.1 The hill-climbing algorithm is described below. The hill-climbing algorithm generates a partial tree/graph. Let's take an example of two-player search tree to understand the working of Alpha-beta pruning. Step 1: At the first step the, Max player will start first move from node A where α= -∞ and β= +∞, these value of alpha and beta passed down to node B where again α= -∞ and β= +∞, and Node B passes the same value to its child D. Introduction. Hill Climbing In Artificial Intelligence is used for optimizing the mathematical view of the given problems. Thus, in the sizable set of imposed inputs and heuristic functions, an algorithm tries to get the possible solution for the given problem in a reasonable allotted time. Hill climbing suits best when there is insufficient ...👉Subscribe to our new channel:https://www.youtube.com/@varunainashots 🔗Link for AI notes: https://rb.gy/9kj1z👩🎓Contributed by: Nisha GuptaHill Climbing ...Future of Artificial Intelligence. Undoubtedly, Artificial Intelligence (AI) is a revolutionary field of computer science, which is ready to become the main component of various emerging technologies like big data, robotics, and IoT. It will continue to act as a technological innovator in the coming years. In just a few years, AI has become a ...Hill-climbing Search >> Drawbacks Hill-climbing search often gets stuck for the following reasons: Local Maxima >> It is a peak that is higher than each of its neighboring states but lower than the global maximum. For 8-queens problem at local minima, each move of a single queen makes the situation worse. Ridges >> Sequence of local maxima ...Say the hidden function is: f (x,y) = 2 if x> 9 & y>9. f (x,y) = 1 if x>9 or y>9 f (x,y) = 0 otherwise. GA Works Well here. Individual = point = (x,y) Mating: something from each so: mate ( {x,y}, {x’,y’}) is {x,y’} and {x’,y}. No mutation Hill-climbing does poorly, GA does well.See full list on cs50.harvard.edu • Steepest ascent, hill-climbing with limited sideways moves, stochastic hill-climbing, first-choice hill-climbing are all incomplete. • Complete: A local search algorithm is complete if it always finds a goal if one exists. • Optimal: A local search algorithm is complete if it always finds the global maximum/minimum.Mar 3, 2022 · Algorithm for Simple Hill Climbing: Step 1: Evaluate the initial state, if it is a goal state then return success and Stop. Step 2: Loop Until a solution is found or there is no new operator left ... Let's take an example of two-player search tree to understand the working of Alpha-beta pruning. Step 1: At the first step the, Max player will start first move from node A where α= -∞ and β= +∞, these value of alpha and beta passed down to node B where again α= -∞ and β= +∞, and Node B passes the same value to its child D. Apr 24, 2021 · hill climbing algorithm with examples#HillClimbing#AI#ArtificialIntelligence HILL CLIMBING: AN INTRODUCTION • Hill Climbing is a heuristic search used for mathematical optimization problems in the field of Artificial Intelligence. • Given a large set of inputs and a good heuristic function, it tries to find a sufficiently good solution to the problem.Let's take an example of two-player search tree to understand the working of Alpha-beta pruning. Step 1: At the first step the, Max player will start first move from node A where α= -∞ and β= +∞, these value of alpha and beta passed down to node B where again α= -∞ and β= +∞, and Node B passes the same value to its child D. Jul 21, 2022 · Hill climbing is basically a search technique or informed search technique having different weights based on real numbers assigned to different nodes, branches, and goals in a path. In AI, machine learning, deep learning, and machine vision, the algorithm is the most important subset. With the help of these algorithms, ( What Are Artificial ... Ex:- Some games like chess, hill climbing, certain design and scheduling problems. Figure 5: AI Search Algorithms Classification (Image designed by Author ) Search algorithm evaluating criteria:Heuristic Search Techniques. Contents • A framework for describing search methods is provided and several general purpose search techniques are discussed. • All are varieties of Heuristic Search: – Generate and test – Hill Climbing – Best First Search – Problem Reduction – Constraint Satisfaction – Means-ends analysis.There are several variations of Hill Climbing, including steepest ascent Hill Climbing, first-choice Hill Climbing, and simulated annealing. In steepest ascent Hill Climbing, the algorithm evaluates all the possible moves from the current solution and selects the one that leads to the best improvement.As far as I understand, the hill climbing algorithm is a local search algorithm that selects any random solution as an initial solution to start the search. Then, should we apply an operation (i.e., ... search. optimization. hill-climbing. Nasser. 201. asked Jan 19, 2018 at 15:07. 1 vote.• Steepest ascent, hill-climbing with limited sideways moves, stochastic hill-climbing, first-choice hill-climbing are all incomplete. • Complete: A local search algorithm is complete if it always finds a goal if one exists. • Optimal: A local search algorithm is complete if it always finds the global maximum/minimum. Artificial Intelligence Methods Graham Kendall Hill Climbing Hill Climbing Hill Climbing - Algorithm 1. Pick a random point in the search space 2. Consider all the neighbours of the current state 3. Choose the neighbour with the best quality and move to that state 4. Repeat 2 thru 4 until all the neighbouring states are of lower quality 5. A node of hill climbing algorithm has two components which are state and value. Hill climbing algorithm is a technique which is used for optimizing the mathematical problems. One of the widely discussed examples of Hill climbing algorithm is Traveling-salesman Problem in which we need to minimize the distance traveled by the salesman.Can’t see past a single move in the state space. Simple Hill Climbing Example TSP - define state space as the set of all possible tours. Operators exchange the position of adjacent cities within the current tour. Heuristic function is the length of a tour. TSP Hill Climb State Space Steepest-Ascent Hill Climbing A variation on simple hill ...Feb 16, 2023 · This information can be in the form of heuristics, estimates of cost, or other relevant data to prioritize which states to expand and explore. Examples of informed search algorithms include A* search, Best-First search, and Greedy search. Example: Greedy Search and Graph Search. Here are some key features of informed search algorithms in AI: There are several variations of Hill Climbing, including steepest ascent Hill Climbing, first-choice Hill Climbing, and simulated annealing. In steepest ascent Hill Climbing, the algorithm evaluates all the possible moves from the current solution and selects the one that leads to the best improvement.May 26, 2022 · In simple words, Hill-Climbing = generate-and-test + heuristics. Let’s look at the Simple Hill climbing algorithm: Define the current state as an initial state. Loop until the goal state is achieved or no more operators can be applied on the current state: Apply an operation to current state and get a new state. Such a technique is called Means-Ends Analysis. Means-Ends Analysis is problem-solving techniques used in Artificial intelligence for limiting search in AI programs. It is a mixture of Backward and forward search technique. The MEA technique was first introduced in 1961 by Allen Newell, and Herbert A. Simon in their problem-solving computer ...Working of Alpha-Beta Pruning: Let's take an example of two-player search tree to understand the working of Alpha-beta pruning. Step 1: At the first step the, Max player will start first move from node A where α= -∞ and β= +∞, these value of alpha and beta passed down to node B where again α= -∞ and β= +∞, and Node B passes the same value to its child D.May 7, 2017 · Hill Climbing Vs. Beam Search • Hill climbing just explores all nodes in one branch until goal found or not being able to explore more nodes. • Beam search explores more than one path together. A factor k is used to determine the number of branches explored at a time. • If k=2, then two branches are explored at a time. May 9, 2021 · Hill-climbing and simulated annealing are examples of local search algorithms. Subscribe Hill climbing algorithm is a local search algorithm which continuously moves in the direction of increasing elevation/value to find the peak of the mountain or best solution to the problem. It terminates when it reaches a peak value where no neighbor has a ... ICS 171 Fall 2006 Summary Heuristics and Optimal search strategies heuristics hill-climbing algorithms Best-First search A*: optimal search using heuristics Properties of A* admissibility, monotonicity, accuracy and dominance efficiency of A* Branch and Bound Iterative deepening A* Automatic generation of heuristics Problem: finding a Minimum Cost Path Previously we wanted an arbitrary path to ...May 9, 2021 · Hill-climbing and simulated annealing are examples of local search algorithms. Subscribe Hill climbing algorithm is a local search algorithm which continuously moves in the direction of increasing elevation/value to find the peak of the mountain or best solution to the problem. It terminates when it reaches a peak value where no neighbor has a ... Following are the types of hill climbing in artificial intelligence: 1. Simple Hill Climbing. One of the simplest approaches is straightforward hill climbing. It carries out an evaluation by examining each neighbor node's state one at a time, considering the current cost, and announcing its current state.This information can be in the form of heuristics, estimates of cost, or other relevant data to prioritize which states to expand and explore. Examples of informed search algorithms include A* search, Best-First search, and Greedy search. Example: Greedy Search and Graph Search. Here are some key features of informed search algorithms in AI:Working of Alpha-Beta Pruning: Let's take an example of two-player search tree to understand the working of Alpha-beta pruning. Step 1: At the first step the, Max player will start first move from node A where α= -∞ and β= +∞, these value of alpha and beta passed down to node B where again α= -∞ and β= +∞, and Node B passes the same value to its child D.Hill-climbing Algorithm In Best-first, replace storage by single node Works if single hill Use restarts if multiple hills Problems: finds local maximum, not global plateaux: large flat regions (happens in BSAT) ridges: fast up ridge, slow on ridge Not complete, not optimal No memory problems Beam Mix of hill-climbing and best first Storage is ...
Mar 3, 2022 · Algorithm for Simple Hill Climbing: Step 1: Evaluate the initial state, if it is a goal state then return success and Stop. Step 2: Loop Until a solution is found or there is no new operator left ... . Kane
Hill-climbing Search The successor function is where the intelligence lies in hill-climbing search It has to be conservative enough to preserve significant “good” portions of the current solution And liberal enough to allow the state space to be preserved without degenerating into a random walk Hill-climbing search Problem: depending on ... Aug 2, 2023 · Following are the types of hill climbing in artificial intelligence: 1. Simple Hill Climbing. One of the simplest approaches is straightforward hill climbing. It carries out an evaluation by examining each neighbor node's state one at a time, considering the current cost, and announcing its current state. Algorithm for Simple Hill Climbing: Step 1: Evaluate the initial state, if it is goal state then return success and Stop. Step 2: Loop Until a solution is found or there is no new operator left to apply. Step 3: Select and apply an operator to the current state. If it is goal state, then return success and quit.There are several variations of Hill Climbing, including steepest ascent Hill Climbing, first-choice Hill Climbing, and simulated annealing. In steepest ascent Hill Climbing, the algorithm evaluates all the possible moves from the current solution and selects the one that leads to the best improvement.Best first search algorithm: Step 1: Place the starting node into the OPEN list. Step 2: If the OPEN list is empty, Stop and return failure. Step 3: Remove the node n, from the OPEN list which has the lowest value of h (n), and places it in the CLOSED list. Step 4: Expand the node n, and generate the successors of node n. Hill-climbing The “biggest” hill in the solution landscape is known as the global maximum. The top of any other hill is known as a local maximum (it’s the highest point in the local area). Standard hill-climbing will tend to get stuck at the top of a local maximum, so we can modify our algorithm to restart the hill-climb if need be.Hill Climbing Algorithm: Hill climbing search is a local search problem. The purpose of the hill climbing search is to climb a hill and reach the topmost peak/ point of that hill. It is based on the heuristic search technique where the person who is climbing up on the hill estimates the direction which will lead him to the highest peak.Can’t see past a single move in the state space. Simple Hill Climbing Example TSP - define state space as the set of all possible tours. Operators exchange the position of adjacent cities within the current tour. Heuristic function is the length of a tour. TSP Hill Climb State Space Steepest-Ascent Hill Climbing A variation on simple hill ...Heuristic Search Techniques. Contents • A framework for describing search methods is provided and several general purpose search techniques are discussed. • All are varieties of Heuristic Search: – Generate and test – Hill Climbing – Best First Search – Problem Reduction – Constraint Satisfaction – Means-ends analysis.Using Computational Intelligence • Heuristic algorithms, ... Illustrative Example Hill-Climbing (assuming maximisation) 1. current_solution = generate initialHill-climbing (or gradient ascent/descent) function Hill-Climbing (problem) returns a state that is a local maximum inputs: problem, a problem local variables: current, a node neighbor, a node current Make-Node(problem.Initial-State) loop do neighbor a highest-valued successor of current if neighbor.Value current.Value then return current.State First, let's talk about the Hill climbing in Artificial intelligence. Hill Climbing Algorithm. It is a technique for optimizing the mathematical problems. Hill Climbing is widely used when a good heuristic is available. It is a local search algorithm that continuously moves in the direction of increasing elevation/value to find the mountain's ...Breadth First Search Ravi Kumar B N, Asst.Prof,CSE,BMSIT 27. Breadth First Search Algorithm: 1. Create a variable called NODE-LIST and set it to initial state 2. Until a goal state is found or NODE-LIST is empty do a. Remove the first element from NODE-LIST and call it E. If NODE- LIST was empty, quit b..