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CAS MA 109 Lecture Notes - Lecture 2: Eulerian Path

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11 Sep 2017

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Boston University

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Mathematics & Statistics

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Document Summary

Collection of dots called nodes and a collection of curves that start and end at nodes. Nodes are sometimes called vertices and the network, graphs. List of edges such that each edge of the list ends at a node where the next edge begins. Starting at node 1, abacgfbe is a path. A path that starts and ends at the same node. Starting at node 1, abacge is a circuit. A circuit that uses each edge of the graph exactly once (so a path that starts and ends at the same node that uses each edge exactly once) Number of edges that start or end at that node. Therefore, if a network has an euler circuit, then every node that is not the start = end node must have even degree. Conjecture: if a network has an euler circuit, then the degree of every node of the network must be an even number.

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Related Questions

Sketch using these guidelines

pul aill al thes information together to sketch graphs that reveal the important You might ask: Why don't we just use a graphing calculator or computer to graph a It's true that modern technology is capable of producing very accurate graphs. But K 21+1+2 features of functions curve? Why do we need to use calculus? even the best graphing devices have to be used intelligently. It is easy to arrive at a misleading graph, or to miss important details of a curve, when relying solely on tech- nology. (See "Graphing Calculators and Computers" at www.stewartcalcelus.com, espe 4 discover the most interesting aspects of graphs and in many cases to and minimum points and inflection points exocily instead of approximately cially Examples 1, 3.4, and 5. See also Section 4.6.) The use of calculus enables us to calculate maximum FIGURE 1 For instance, Figure I shows the gr aph of /(x)-è¨-21x, + 18x + 2.At first glance it seems reasonable: It has the same shape as cubic curves like y x and it appears to have no maximum or minimum point. But if you compute the derivative, you will see that there is a maximum when x-0.75 and a minimum when x 1. Indeed if we zoom in to this portion of the graph, we see that behavior exhibited in Pigure 2 Without calculus, we could easily have overlooked it. 6a, FIGURE 2 In the next section we will graph functions by using the interaction between calculus and graphing devices. In this section we draw graphs by first considering the foilowing information. We don't assume that you have a graphing device, but if you do have one you should use it as a check on your work. â Guidelines for Sketching a Curve every item is relevant to every function. (For instance, a to make a sketch that displays the most important aspects of the function. The following checklist is intended as a guide to sketching a curve y- f(x) by hand. Not given curve might not have an asymptote or possess symmetry.) But the guidelines provide all the information you need A. Domain It's often useful to start by determining the domain D of f, that is, the set B. Intercepts The y-intercept is f(o) and this tells us where the curve intersects the of values of x for which f(x) is defined y-axis. To find the x-intercepts, we set y-0and solve for xã(You can omit this step if the equation is difficult to solve.) ry (a) Even fusction: reflectional symmetry all x in D, that is, the equation of the curve is unchanged when x is replacea by -x, then f is an even function and the curve is symmetric about the y-axis. This means that our work is cut in half. If we know what the curve looks like for 0, then we need only reflect about the y-axis to obtain the com- plete curve [see Figure 3(a). Here are some examples: y-ey-ry x). and for all x in D, then f is an odd function and the curve is symmetric about the origin. Again we can obtain the complete curve if we know what it looks like for x0. [Rotate 180Â° about the origin; see Figure 3(b).] Some b) Oud function rotational symmetry FIGURE 3 simple examples of odd functions are y-xy-x'y - and y-sin

Problem 3

Math 151 - Sections 34, 35, 36 - Workshop 11 This workshop deals with an addition formula in section 5.1. This formula is related to an ld story about the great mathematician Gauss. Here is one version of the story Wh en Gauss was ten years old, he attended a certain math class with other kids. One fine day, the math teacher discovered that he was running out of time to grade the latest batch of math homeworks. This is why he decided to finish the grading during his math lecture period. To keep the students busy while he graded, he gave them the following task at the start of the period: Use your slate (the small personal blackboard that every student had in class) to add up the numbers 1,2,3,... , 100 Seconds after the teacher gave this in-class assignment, little Gauss pointed to his slate and yelled "Here is the answer." Then Gauss did nothing for an hour, while the other students labored with the additions and the teacher graded. At the end of the period Gauss showed the correct answer 5050 on his slate. Only Gauss got the correct answer Then Gauss told everybody that the sum 1+2+3+ + 100 is ( 1 + 100) + (2+99)+ (2+98)+--+ (50+51) = 101 + 101 + 101 +. . . +10 101. 50-5050 Problem 1. Explain carefully what Gauss had done. Include the reason why it is impor tant that 100 happens to be Problem 2. Let N be an even positive integer. Use the method of Problem 1 to prov the formula 1 +2+3+.+N) be an even number Problem 3. The formula is still valid when N is an odd integer. Prove this, using a variation on the argument given by Gauss The story continues: Gauss then gave the class a lecture on how his method could be used to sum an arithmeric series (a+1.b) + (a+2 b) + (a+3.b)+. + (a + N b), where a and b are constants Problem 4. Find a formula for the sum (a+1.b)+(a+2.b)+ (a +3.b)+(a+ N b) Prove this formula the way Gauss would have done it. You have to do the case when N is even and the case when N is odd Now let us consider a fictional alternate history where Gauss had not thought of this ve clever trick. We can imagine the ten year old Gauss going home and doing the sequential computations 1+2 1+2+3 1+2+3+4 1+2+3+4+5 and so forth, just to see if he could find a pattern in the sequence of answers. He would have discovered somethin like this: once he had the sum 1+2+3++N, he could simply add N+1 to that sum, and that would give him the sum 1+2+3 Now assume that, by trial and error, Gauss discovered that the formula 1+2+3+ +N an even numbe +) Include the reason why it is important that +Â·Â·Â· + (N +1) very quickly is true for several values of N. How could he prove that the formula is really true for ALL N? The insight described in the previous paragraph might have led Gauss to think the following: All he had to do was prove N(N+1) Â± (N + 1) other words, he only needed to show: Formula for 1 + 2+3+.+ N plus N +1 equals formula for 1+2+3+(N+1). He would have discovered the principle of mathematical induction Problem 5. Prove of the formula for 1+2 +3+... + N (N +1)(+1X++1) Show how this leads to a proof N(N+1 N+)

Complete problem 3 using the information above.

Math 151 Sections 34, 35, 36 Workshop 11 ted to arn This workshop deals with an addition formula in section 5.1. This formula is rel oft told story about the great mathematician Gauss. Here is one version of the story When Gauss was ten years old, he attended a certain math class with other kids. One fine day, the math teacher discovered that he was running out of time to grade the latest batch of math homeworks. This is why he decided to finish the grading during his math period. To keep the students busy while he graded, he gave them the following task at th of the period: Use your slate (the small personal blackboard that every student had start in class) to add up the numbers 1,2,3,... , 100 Seconds after the teacher gave this in-class assignment, little Gauss pointed to his slate Here is the answer." Then Gauss did nothing for an hour, while the other students labored with the additions and the teacher graded. At the end of the perioc Gauss showed the correct answer 5050 on his slate. Only Gauss got the correct answer. Then Gauss told everybody that the sum 12 +3.+ 100 is (1+100)+(2+99) + (3498)+ Problem 1. Explain carefully what Gauss had done. Include the reason why it is impor tant that 100 happens to be an even number Problem 2. Let N be an even positive integer. Use the method of Problem 1 to prove the formula 1 +2 +3+.. . +N(N. Include the reason why it is important that N +(50+51) = 101 + 101 +101 + +101-101.50-5050 an even number. Problem 3. The formula is still valid when N is an odd integer. Prove this, using a variation on the argument given by Gauss The story continues: Gauss then gave the class a lecture on how his method could be used to sum an arithmeric series (a +1.b) (a +2.b) (a +3.b)+. (a +N b), where a and b are constants Problem 4. Find a formula for the sum (a+1.b)+ (a+2.b) + (a +3.b)+ +(a+ N.b) Prove this formula the way Gauss would have done it. You have to do the case when N is even and the case when N is odd Now let us consider a fictional alternate history where Gauss had not thought of this very clever trick. We can imagine the ten year old Gauss going home and doing the sequential computations 1+2 1+2+3 1+2+3+4 1+2+3+4+5 and so forth, just to see if he could find a pattern in the sequence of answers. He would have discovered somethin like this: once he had the sum 1+2+3+...+ N, he could simply add N +1 to that sum and that would give him the sum 1+2+3+ + (N +1) very quickly Now ass N(N+1 ume that, by trial and error, Gauss discovered that the formula 1+2+3+ is true for several values of N. How could he prove that the formula is r for ALL N? The insight described in the previous paragraph might have led Gauss to other words, he only needed to show: Formula for 1+2+3+ + N plus N +1 equals formula for 1+2+3++N+1). He would have discovered the principle of mathema -.. + N eally true 1)+1) think the following: All he had to do was prove mm) + (N + 1) NN+1 (N+1)(( In ered the principle of mathematical induction Problem 5. Prove N(N+1) (N + 1 of the formula for 1+2+3+.+N. (Nt1MNHHI) Show how this leads to a uCtion a proof