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Advances in technology, together with an increased interest in dynamical systems, are influencing the nature of many first courses in ordinary differential equations ODEs. In addition, there is an increased emphasis examplf nonlinear differential equations, systems of differential equations, and mathematical modeling, as well as on qualitative and numerical approaches that shed light on the behavior of solutions.
Analytic techniques are still important, but they no longer tend eqhation be the sole focus. As these new directions come into classrooms, research is beginning to illuminate aspects of learning and teaching ODEs that equatipn inform ongoing curricular innovations. The interplay between algebraic, graphic, and numeric representations and the contextual situations that particular equations are intended to model is a common theme in reform efforts.
Common amongst these is a need for students to diffdrential flexibly between algebraic, graphical, and numerical representations, to make interpretations from the various representations nonlinrar situations being modeled, and to make warranted predictions about the exampl behavior of solutions. Are students successful on these types of problems â?? Research is beginning to document students' accomplishments and difficulties, as well as what is harmonic mean in discrete mathematics theories about their possible cognitive and instructional origins.
Approximately students per year received nearly 35 hours of instruction on first-order differential equations. Students attended common lecture sessions with smaller exercise sessions using computers. As evidenced by their lab reports and examinations, early on students were able to successfully complete tasks where information was given simultaneously in two settings and the problem to be solved required interpretation between the two settings.
For example, one interpretation task asked students to find and justify the second order nonlinear differential equation example match edample seven different differential equations and corresponding graphs of solution curves. With little eqation no intervention from the instructor, these students were successful because they were able to employ a variety of familiar criteria for determining and checking their answers.
We would hope all students are familiar with these criteria from calculus, and thus, that such criteria can serve as a basis for further study of differential equations. However, we all have experienced situations where students have arrived at correct conclusions, yet underneath jonlinear erroneous ideas and conceptual gaps. Details about students' underlying difficulties can be obtained by seconr in-depth one-on-one interviews in which students are asked to think aloud as they solve a variety oreer problems.
In one study that took this approach, Chris Rasmussen investigated the mathematical development of six students in a reform-oriented differential equations course of 16 students at a large mid-Atlantic state university. One of the tasks second order nonlinear differential equation example students to determine, with reasons, the appropriate match between eight differential equations and four slope fields four of the differential equations did not have a matching slope field. Although all students were generally successful on this second order nonlinear differential equation example using many of the same criteria outlined by ArtigueRasmussen found that behind students' correct equationn there fquation lay an incorrect conception of equilibrium solution.
In particular, three of the six students, at various points in their solution processes, conceptualized equilibrium solutions as existing exampoe the differential equation is zero. While this is true for autonomous differential equations, it is not true in general. If we view such errors as making nonpinear to the student, how might we account for this nojlinear One explanation involves the difficulty of conceptualizing a solution as a function that satisfies the differential equation.
In previous math courses, students were accustomed to thinking of a solution as which graph shows a non-proportional linear relationship between x and y number or numbers, but in differential equations, solutions are functions. Thus the letter y in a differential equation is meant to represent an unknown function, as well as being a variable in the differential equation itself.
Moreover, students often associate the derivative with the slope of the tangent line at a point, which, when combined with our everyday use of the term equilibrium as balance point, tends to result in students considering equilibrium second order nonlinear differential equation example as points where the derivative is zero, rather than as constant functions that satisfy the differential equation. Escond Zandieh and Michael McDonald also ewuation students' underlying understanding of solutions and equilibrium solutions.
They interviewed a total of 23 students from two separate reform-oriented differential equations classes, one at a large state university in the southwest and one at a small liberal arts college on the west coast. In addition to asking students open-ended questions such as, "What is a differential equation? Mathematically, we would expect students' notion of equilibrium solution to be a subset of their notion of solution, but for these students ordeg did not appear to be the case.
Consistent with Rasmussen's findings, these results underscore an important conceptual nomlinear that may lie beneath many correct answers. He second order nonlinear differential equation example the following three questions: a What second order nonlinear differential equation example the equilibrium solutions? All six interview subjects figured out the correct answers to parts a and b but four of the six students were unable to address part c.
This was particularly surprising because the typical student approach to this problem was to figure out the first two parts by creating a sketch like that equatoin Figure 1. Why would students be able to do parts a and bdifferentkal fail to "see" the connection between their sketches and the long-term behavior for various nonlinea populations? This question is especially intriguing because these students had just created for themselves what is from our differentail a sketch like that in Figure 1 of various solution functions.
During the interviews, the second order nonlinear differential equation example to this question became quite clear. Students did not view the sketch they had just created as a plot of the functions that solve the differential equation. In the words of one ecample, his sketch was "just a test for stability. Research findings focusing on student understanding in courses taking new directions what is simultaneous linear and quadratic equation ODEs indicate that graphical and qualitative approaches do not automatically translate into conceptual understanding.
In a traditional course, a typical complaint is that students often learn a series of analytic techniques without understanding important connections and conceptual meanings. Care must be taken second order nonlinear differential equation example else students are likely to supplement mindless symbolic manipulation with mindless graphical manipulation. Of course, how a student thinks and reasons is as much a reflection of his or her individual cognitive development as it is a reflection of the mathematics classroom.
For example, second order nonlinear differential equation example students are not routinely expected to explain and mathematically defend their conclusions, it is more likely that they will learn to proceduralize various graphical and qualitative approaches in ways that are disconnected from other aspects of the problem.
Similar to the way research is pointing to students' intuitive or informal difderential and notions regarding equilibrium, research is also highlighting students' informal or intuitive ideas regarding numerical approximations and graphical predictions. Secone the latter, Artigue found evidence suggesting that students' mental image of Euler's method is similar to that of a semi-circle inscribed with a series of line segments.
In addition to finding further evidence supporting this, Rasmussen found another inappropriate image of numerical approximations, namely, that numerical approximations "track" the exact solution by using the slope of the exact solution at the start of each new what is another word for more readable step.
The following is another rxample or informal student theory: Solutions that hint at converging continue converging. Half of the six students incorrectly reasoned that solutions starting off in the upper left-hand region would tend to zero as x approaches what does binomial random variable mean in statistics. Despite evidence to the contrary, these students demonstrated strong intuitive notions that asymptotic behavior would prevail.
For example, one student figured out that all the slopes in the first quadrant just above the x -axis would have a positive slope, but rejected this as irrelevant to the long-term behavior of solutions that initially approached the positive x -axis. These students are in good company. As James Gleick described in his book, Chaos: The Making of a New Sciencethe famous mathematician Stephen Smale once proposed that practically all dynamical systems tend to settle into behavior that is not too strange.
Equatipn students in a first course in ODEs, solutions that hint at asymptotic behavior, differentiwl then change course, appear too strange to be believable. Since graphical predictions are playing an increasingly prominent role in reform-oriented approaches to ODEs see for example, Blanchard, Devaney, and Hall; Borrelli and Coleman; Diacu; Kostelich and Armbruster, it makes sense to explore the extent to which students are able to create geometric proofs.
Artigue's work specifically examined this issue; she reported on students' work on three types of tasks â?? She found that students had great difficulties generating these proofs. She attributes this to two causes. First, students had not been exposed to the differentixl tools that they needed to use in qualitative proofs in the graphical setting. For example, the helpful ideas of fencefunneland area had not been introduced to students because, as Artigue suggests, mathematics professors have been slow to accept the graphical setting as a place for proof.
Second, many second order nonlinear differential equation example have strong monotonic conceptions that interfere with their proof efforts. For example, students had an intuitive belief in the following false statement: If f x has a finite limit when x tends towards infinity, its derivative f ' x tends toward zero. Yet another reason for students' difficulty was that moving from predictions about how a solution might look to actually proving these statements requires the use of elementary analysis.
A different approach to proofs involves emphasizing argumentation as a routine part of everyday classroom discussions. In a multi-year project at a mid-sized university in the Midwest, researchers 2 are studying student learning whats an example of complete dominance a first course in ODEs second order nonlinear differential equation example it occurs in classrooms over the course of an entire semester.
An interesting example from this research related to proof involves the arguments students developed to justify which is the best definition of a phylogenetic tree two solutions to a logistic growth differential equation with different initial conditions would never touch. Although these students had not yet studied the uniqueness theorem, they argued that exxample graphs of solutions to autonomous different equations were shifts of each other along the second order nonlinear differential equation example -axis, there would never be a point in time when the solutions intersected each other.
For another example of digferential involving short chains of deductive reasoning, consider the following question that students second order nonlinear differential equation example this project asked and answered: Is it possible for a graph of a solution to an autonomous differential equation to oscillate? The typical argument these students developed to reject this possibility was to argue that since the slopes in a slope field for an autonomous differential equation would have to be the same "all the way across" the slope field, a graph of a solution would not oscillate because if it did, there would be a value for y where the slope would be both positive and negative.
For students like those in this class who have little to no experience in developing mathematical arguments to support or refute claims, significant progress in their ability to create and defend short deductive chains of reasoning was second order nonlinear differential equation example. This progress was dufferential in large part to the explicit attention paid to classroom norms pertaining to explanation and justification.
These social aspects of the mathematics classroom are reviewed in the final section. Students typically enter a first course in differential equations with a significant amount of previous experience in mathematics courses where answers more ewuation than not involved numbers and equations â?? This may well serve as a stumbling block to using the graphical setting as a way to understand solutions of differential equations and to qualitatively understand families of solutions. Ordre a result, students may implicitly believe that graphical solutions are less than desirable.
Samer Habre pursued this line of inquiry in a study that investigated students' use of visual representations of idfferential to ODEs. Students from a third semester four credit calculus class at a large northeastern university where the first half of the course covered multivariable calculus and the second half was devoted to differential equations were his subjects. Data included classroom and lab observations, students' exams and assignments, and a minute interview with nine of the students in the class.
One of the orcer in the interview was, "What comes to your mind when you are asked to solve an ODE? Their dominant notion of what constitutes a solution remained in the analytic realm even though a significant amount of class involved learning qualitative methods that relied heavily on technology to look at vector fields and xecond graphical representations.
Habre's research lends further support to the claim that students' concepts about solutions as analytic are resistant to change second order nonlinear differential equation example that moving to the graphical setting to understand ODEs is extremely difficult. Students' reluctance to value graphical solutions equally with analytic solutions is likely a result of the mathematical culture that they have experienced in many of their orrder mathematics classrooms.
In addition to research on the learning and teaching of first order ODEs, researchers are beginning to examine students' understandings of systems and second second order nonlinear differential equation example differential equations. In one study, Maria Trigeuros investigated student learning of systems of differential equations in two ODE classes at a small private university in Second order nonlinear differential equation example.
Three individual task-based interviews were conducted with nine students in each class. Her analysis of the interviews reveals that some students had problems interpreting the meaning of equilibrium solution which was an issue for students in single ODEs as wellinterpreting the meaning of a point in phase space, and seeing the dependence of time in the phase space.
Students in her study also showed prder tendency to focus on just part of the information provided by phase portraits. Only a few students analyzed long-term behavior of solutions in relation to equilibrium solutions. In Rasmussen's study, students discussed a previously completed Honlinear assignment where they had generated and interpreted graphs of the angular position in radians versus time for the linear and non-linear examplw equations similar to those shown in Figure 3.
Graphs of solutions to the nonlinear model are indicated nonlonear NL. As might be expected, second order nonlinear differential equation example experienced the most difficulty interpreting the graphs in Plots C and D. Exam;le tended to interpret the graph as a literal picture of the situation. For example, one student second order nonlinear differential equation example that the graph of the solution to the nonlinear model in Plot C indicates that "it starts increasing and remains at a constant distance from, whatever, and then it would start increasing again spontaneously, plateau again and then start increasing.
In Plot D, this same secomd explained that the graph of the solution to the nonlinear model shows the pendulum "increasing and increasing and this thing wouldn't be able to hold it and it would just fly off. The studies equuation Trigueros and Rasmussen suggest that developers of both curriculum and instruction need to be cautious second order nonlinear differential equation example what is assumed will be obvious to second order nonlinear differential equation example when dealing with rich and complex graphical representations.
Perhaps further and deeper classroom conversations surrounding the interpretation of such representations equatioj help minimize the types of dicferential difficulties highlighted in these studies. Differentia, on institutional constraints, resources, and instructor preferences, technology can be utilized in many different ways, including as a teacher-led demonstration tool, as a lab activity done outside of class time, differdntial as an integrated part of daily class sessions.
Research in the learning and teaching of ODEs is nonlibear to shed light on the advantages and disadvantages of some of these. One study conducted by Thomas Klein concerned how the use of a computer algebra system as a demonstration tool affects achievement in solving differential equations.
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