What is Differential equations: Definition and 999 Discussions

In mathematics, a differential equation is an equation that relates one or more functions and their derivatives. In applications, the functions generally represent physical quantities, the derivatives represent their rates of change, and the differential equation defines a relationship between the two. Such relations are common; therefore, differential equations play a prominent role in many disciplines including engineering, physics, economics, and biology.
Mainly the study of differential equations consists of the study of their solutions (the set of functions that satisfy each equation), and of the properties of their solutions. Only the simplest differential equations are solvable by explicit formulas; however, many properties of solutions of a given differential equation may be determined without computing them exactly.
Often when a closed-form expression for the solutions is not available, solutions may be approximated numerically using computers. The theory of dynamical systems puts emphasis on qualitative analysis of systems described by differential equations, while many numerical methods have been developed to determine solutions with a given degree of accuracy.

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  1. Tapias5000

    How to solve this application problem in edo?

    Summary:: A nitric acid solution enters at a constant rate of 6 liters / minute into a large tank that originally contained 200 liters of a 0.5% nitric acid solution. The solution inside the tank is kept well stirred and leaves the tank at a rate of 8 liters / minute. If the solution entering...
  2. S

    MHB Solve Differential Eq: xe^-1/(k+e^-1) for x, k, t

    The number of organisms in a population at time t is denoted by x. Treating x as a continuous variable, the differential equation satisfied by x and t is dx/dt= xe^-1/(k+e^-1), where k is a positive constant.. Given that x =10 when t=0 solve the differential equation, obtaining a relation...
  3. L

    I Solve second order linear differential equation

    Consider the second order linear ODE with parameters ##a, b##: $$ xy'' + (b-x)y' - ay = 0 $$ By considering the series solution ##y=\sum c_mx^m##, I have obtained two solutions of the following form: $$ \begin{aligned} y_1 &= M(x, a, b) \\ y_2 &= x^{1-b}M(x, a-b+1, 2-b) \\ \end{aligned} $$...
  4. N

    B Basic Idea of Differential Equations

    Hello. After a lot of researching, I am still not clear how the subject of differential equations is really any different from derivatives and integrals which are learned in the main part of calculus. For example: "Population growth of rabbits: N = the population of rabbits at any time t r=...
  5. chwala

    Clarifying the Use of Integrating Factors in Exact Differential Equations

    I am looking at this and i would like some clarity... at the step where "he let" ##μ_y##=0" Could we also use the approach, ##μ_x##=0"? so that we now have, ##μ_y##M=μ(##N_{x} -M_{y})##... and so on, is this also correct?
  6. guyvsdcsniper

    Courses Where to go after Differential Equations?

    I am currently pursuing a Bachelors in Physics. With my current work experience, that degree will eventually allow me to reach an engineering position in Non Destructive Testing. While I enjoy the career field I believe I could do more with my degree. I personally would like to work at LHC or...
  7. AHSAN MUJTABA

    A Phase Portraits of a system of differential equations

    One thing that bothers me regarding the phase portraits, if I plot a phase portrait, then all my possible solutions (for different initial conditions) are included in the diagram? In other words, a phase portrait of a system of ODE's is its characteristic diagram?
  8. greg_rack

    Learning DEs: Solving 2nd Order Differential Equations

    Hi guys, I have just started studying DEs on my own, so pardonne moi in advance for the probably silly question :) Via Newton's second law of motion: $$x''=\frac{F}{m} \ [1]$$ Which is a second-order differential equation. But, from here, how do I get the good old equation of motion...
  9. greg_rack

    B Real world applications of differential equations

    Hi guys, how are you doing? My maths teacher asked me to work on and deliver an engaging insight-oriented "lesson" to my class, about physical/engineering and real-world applications of differential equations, in order to better get the meaning of operating with such mathematical objects. Of...
  10. E

    Studying Need some advice -- Studying oscillations before differential equations?

    Hello there, I need some advice here. I am currently studying intro physics together with calculus. I am currently on intro to oscillatory motion and waves (physics-wise) and parametric curves (calc/math-wise). I noticed that in the oscillatory motion section, I need differential equation...
  11. Falgun

    Applied Ordinary Differential Equations Books

    I am trying to self study Ordinary Differential Equations and am totally fed up of "cookbook style ODEs". I have recently finished Hubbard's Multivariable Calculus Book and Strang's Linear algebra book. I would like a rigorous and Comprehensive book on ODEs. I have shortlisted a few books below...
  12. yucheng

    Simmons 7.10 & 7.11: Find Curves Intersecting at Angle pi/4

    >10. Let a family of curves be integral curves of a differential equation ##y^{\prime}=f(x, y) .## Let a second family have the property that at each point ##P=(x, y)## the angle from the curve of the first family through ##P## to the curve of the second family through ##P## is ##\alpha .## Show...
  13. V

    Solve the system of differential equations

    I have my set of differential equations which is dx/dt = -2x, dy/dt=-y+x2, with the initial conditions x(0)=x0 and y(0)=y0. I'm a little confused about how to approach this problem. I thought at first I would differentiate both sides of dx/dt = -2x in order to get d2x/dt2 = -2, and then I would...
  14. JD_PM

    Solving a system of differential equations

    Summary:: We want to find explicit functions ##g(y,t)## and ##f(y,t)## satisfying the following system of differential equations. I attached a very similar solved example. Given the following system of differential equations (assuming ##y \neq 0##) \begin{equation*} -y\partial_t \left(...
  15. P

    I Solving a system of differential equations by elimination

    I would to know if I'm solving system differential equation by elimination correctly. Could somebody check my sample task and tell if something is wrong?
  16. yucheng

    Applied Is Piaggio's Differential Equations worth reading?

    I got to know of this book through Freeman Dyson's obituary. Just wondering, is it useful in studying Physics (it seems to cover everything), do people even use it these days? I understand differential equations are basically half of Physics. By the way, this book is really old, are there any...
  17. R

    I Is it possible to solve such a differential equation?

    Hello, I would like to is it possible to solve such a differential equation (I would like to know the z(x) function): \displaystyle{ \frac{z}{z+dz}= \frac{(x+dx)d(x+dx)}{xdx}} I separated variables z,x to integrate it some way. Then I would get this z(x) function. My idea is to find such...
  18. A

    Maple Is there a solution for these three differential equations?

    I have three differential equations with three unknowns ##p##, ##q## and ##r##: $$\displaystyle {\frac {\partial }{\partial p}}\sum _{k=1}^{5}f_{{k}}\ln \left( P \left( X=k \right) \right) =0$$, $$\displaystyle {\frac {\partial }{\partial q}}\sum _{k=1}^{5}f_{{k}}\ln \left( P \left( X=k...
  19. docnet

    System of two differential equations

    The first equation leads to x = ae^2t + be^t and the second equation leads to y=[1/(ln(sint+pi/2)+c)] this corresponds to the system a+b=1/c 2a+b=1 which has infinitely many solutions. what am I missing here?
  20. WyattKEllis

    Diff. Eq. — Identifying Particular Solution Given solution family

    I identified the root 1 with multiplicity 1 and the root 2 with multiplicity 1. So The characteristic equation is ((m-1)^2)*(m-2)=0. Simplifying and substituting with y I found: y'''-4y''+5y'-2y=0. So now I've realized that this is actually describing y(t)=(C1)*(e^t)+(C2)*(e^t)+(C3)*(e^2t) and...
  21. Ron Burgundypants

    Second order differential equation solution

    I know the solution to the equation (1) below can be written in terms of exponential functions or sin and cos as in (2). But I can't remember exactly how to get there using separation of variables. If I separate the quotient on the left and bring a Psi across, aka separation of variables (as I...
  22. M

    MHB Null Cline Solutions for Differential Equations: Help Needed!

    I was wondering if anyone could help me clarify which null cline solutions are correct for this question I've got: I've got two differential equations: \[ du/dt =u(1-u)(a+u)-uv \] \[ dv/dt = buv-cv \] where a, b and c are constants. I know to find the u null clines you set du/dt to 0. \[...
  23. C

    Mathematical Engineer, Electrical Engineer, & Author

    My History -------------- I attended Oregon State U. and majored 3 years in Electrical Engineering. Then I switched to a Math major for my final years and graduated with a B.S. in Math (1967). Developed several Apps for Engineers & Scientists. My first job was with Lockheed Aircraft Co...
  24. Kaguro

    Mixed method of solving differential equations

    I use the operator method here: (D^2 + D+3)y = 5cos(2x+3) ## y = \frac{1}{D^2+D+3} 5cos(2x+3) ## ## \Rightarrow y= \frac{5}{-(2)^2+D+3}cos(2x+3) ## ## \Rightarrow y= \frac{5}{-4+D+3}cos(2x+3) ## ## \Rightarrow y= \frac{5}{D-1}cos(2x+3) ## At this, if I revert back to write: (D-1)y = 5cos(2x+3)...
  25. T

    I Vector space for solutions of differential equations

    Good Morning Recently, I asked why there must be two possible solutions to a second order differential equation. I was very happy with the discussion and learned a lot -- thank you. In it, someone wrote: " It is a theorem in mathematics that the set of all functions that are solutions of a...
  26. A

    A Differential Equations (Control Optimization Problem)

    \begin{equation} y_{1}{}'=y_1{}+y_{2} \end{equation} \begin{equation} y_{2}{}'=y_2{}+u \end{equation} build a control \begin{equation} u \epsilon L^{2} (0,1) \end{equation} for the care of the appropriate system solution \begin{equation} y_{1}(0)=y_{2}(0)=0 \end{equation} satisfy...
  27. A

    MHB Optimal Control for Differential Equations with L2 Control Constraint

    To be able to build a control y_{1}{}'=y_1{}+y_{2} y_{2}{}'=y_2{}+u u \epsilon L^{2} (0,1) for the care of the appropriate system solution y_{1}(0)=y_{2}(0)=0 satisfy y_{1}(1)=1 ,y_{2}(1)=0 Please kindly if you can help me Discipline is Optimal ControlHELP! i need to find...
  28. J

    Studying Ordinary Differential Equations and Calc III

    Hello, I need help deciding on whether to take ODE (MAP2302) and Calc III during the summer. Would it be wise to take ODE along with Calc III in the same semester? Some people have told me to take Calc III first because there are a few things in ODE that are taught in Calc III, but others have...
  29. A

    A Predicting how far an object will fly

    Hi, I have an experimental setup where we are taking certain different types of metals of varying shapes and sizes, weighing them, taking approximate measurements, and then blowing it off of a table of a fixed height with an Air Nozzle. The data taken down in experiment is the PSI at which the...
  30. K

    B Differential equations in physics

    Can someone list to me (and whoever is going to view this thread) what topics in differential equations should be studied so that we can have a decent knowledge of the general physical theories in which they occur? (And I believe, they appear in all theories.) So far, I believe the two most...
  31. A

    Differential Equations and Damper Curves

    Good evening, I have been wrestling with the following and thought I would ask for help. I am trying to come up with the equations of motion and energy stored in individual suspension components when a wheel is fired towards the car but, there is a twist! I am assuming a quarter car type...
  32. V

    Courses Is it Worth Retaking a "C" in Differential Equations?

    I got a C last semester in elementary differential equations. It was an online class using ProctorU and I always had technical difficulties, so while my homework category was a 95% my test category was around a 60%. I am a spring-semester sophomore right now and my GPA is 3.611. If I retake...
  33. J

    Heating a soup (solving this problem with a DE)

    I'm having quite a bit of a problem with this one. I've managed to figure out that ##T_0 = 0##. However, not knowing what ##q(t)## is bothers me, although it seems that I could theoretically solve the problem without knowing it. For ##t>t_1##, integration by parts gives me ##T = Ce^{-t/10}##...
  34. Muskyboi

    [Differential equations] Mixing problem.

    v(t)=600+(9-6)t =600+3t 1500=600+3t therefore t=300 hrs when tank is full Cin=1/5(1 + cost) ds/dt=Rate in - rate out = CinRin - Cout*S(t)/V(t) =1/5(1 + cost)*9 - 6*S(t)/(600+3t) S(0)=5 ib Solving the first order linear ODE we get: https://www.desmos.com/calculator/l7iixzgyll therefore...
  35. A

    Partial Differential Equations result -- How to simplify trig series?

    Solve the boundary value problem Given u_{t}=u_{xx} u(0, t) = u(\pi ,t)=0 u(x, 0) = f(x) f(x)=\left\{\begin{matrix} x; 0 < x < \frac{\pi}{2}\\ \pi-x; \frac{\pi}{2} < x < \pi \end{matrix}\right. L is π - 0=π λ = α2 since 0 and -α lead to trivial solutions Let u = XT X{T}'={X}''T...
  36. J

    I Solving Differential Equations in General Relativity

    In genaral relativity, how to solve differential equations is seldom be discussed. I want to know how to sole the differential equations like this: $$\partial_kv^i(x)+\Gamma^i_{jk}(x)v^j(x)=\partial_kA^i(x)$$ Here ##\Gamma^i_{jk}(x)## is connection field on a manifod and ##A^i(x)## is a vector...
  37. L

    Green's functions (Fourier Series)

    In order to obtain equation (3), I think I have to do the Fourier transform in the x direction: \begin{equation} \tilde{G}(k,y,x_0,y_0) = \int_{- \infty}^{\infty} G(x,y,x_0,y_0) e^{-i k x} dx \end{equation} So I have: \begin{equation} -k ^2 \tilde{G}(k,y,x_0,y_0) + \frac{\partial^2...
  38. kepherax

    Cauchy-Euler with x=e^t? Differential Equations (ODE)

    I'm fine with this up to a certain point, but I'm not certain if I'm using the substitution correctly. After finding the homogeneous solution do I plug in x= e^t in the original equation and then divide by e^2t to put it in standard form before applying variation of parameters so f=1, or do I...
  39. T

    Coupled linear stochastic differential equations

    In order to solve for ##x##, I need to re-write the equation for ##dx## so it is independent of ##y## and ##dy##. However, I am having some issues with this. Can someone give me a push in the right direction?
  40. P

    How do I solve these differential equations?

    For the first and second, I don't know if there is an analytical solution. The third I believe can only be solved with: $$ f(x,t)=c e^{\alpha \beta t}$$
  41. akin-iii

    I How do I derive a PDE for the volume flow rate of a tilting vessel?

    So the other day, I was pouring beer from a can to a mug and I obviously know the flow rate depends on the height of the beer from the bottom of the can (fluid level in the vessel), angle of tilt and I think time as well. I was wondering how to best model the PDE to describe such a phenomenon (...
  42. S

    Set up the differential equation showing the voltage V(t) for this RC circuit

    Hi all. I have another exam question that I am not so sure about. I've solved similar problems in textbooks but I have a feeling once again that the correct way to solve this problem is much simpler and eluding me. Especially because my answer to a) is already the solution to c) and d) (I did...
  43. K

    I Find Practical Resonance Frequencies in Linear Differential Equations

    Hi all, I would like to know what is the equation upon which I can use to determine the practical resonance frequencies in a system of second order, linear differential equations. First some definitions: What I mean by practical resonance frequencies, is the frequencies that a second order...
  44. M

    I Projective Methods For Stiff Differential Equations

    Good evening, https://pdfs.semanticscholar.org/688b/e703a59a4a0c6fc96b4e42c38c321cd4d5b8.pdf Do you know :PROJECTIVE METHODS FOR STIFF DIFFERENTIAL EQUATIONS I have to make a program to solve a first-order differential equation according to this method but I do not arrive despite my efforts...
  45. D

    Need help with Matlab Function of Differential Equations

    WHAT HAPPENS IS That I need to model the example of A Protein G example, using a function f in Matlab, but when I execute the script, the graphics I get do not correspond to those of the example. The problem is that I can not understand what the model seeks to represent, besides that I do not...
  46. M

    MHB Projective Methods for Stiff Differential Equations

    hello, now I'm working on a numerical method called: Projective Methods for Stiff Differential Equations: Problems with Gaps in Their Eigenvalue Spectrum. but I can not understand despite the hours of work that I spent on it I turn to you for help, applying this method on this exmple : y '= y...
  47. I

    I What is a symmetric ODE / what does it mean when an ODE is symmetric?

    How can an ODE be symmetric? How would you plot an ODE to show off this property? (i.e. what would be the axes?)
  48. F

    I Separation of Variables for Partial Differential Equations

    When using the separation of variable for partial differential equations, we assume the solution takes the form u(x,t) = v(x)*g(t). What is the justification for this?
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