Results 1 to 4 of 4

Math Help - DE URGENT Help

  1. #1
    Junior Member
    Joined
    Aug 2008
    Posts
    27

    DE URGENT Help

    Ok, I have to solve this using a computer program but if someone can just explain the question to me that would be a start.

    y'(t)=-20y+e^-t

    Solve for 0t10 using the forward Euler with time-step 0.1, i.e. write the derivative in terms of y(t) and y(t+dt), with the time set to t on the right hand side, and solve y(t+dt) to set up the update scheme.

    I've read up on the Euler's forward scheme but still don't understand what the question is asking or how to go about it!
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Newbie
    Joined
    Feb 2009
    Posts
    4
    \mathsf{f(t,y)=\frac{dy}{dt}=-20y+e^{-t}}

    Eulers method basically boils down to:

    \mathsf{y_{i+1}=y_i+f(y_i,t_i)\cdot \Delta t}

    Where your \mathsf{\Delta t} is your time step and each forward y value is calculated from the current time t, the current y value and the time step.

    For the specific case you've stated:

    \mathsf{y_{i+1}=y_i+\left(-20y_i+e^{-t_i}\right)\cdot \Delta t}

    If put that into a spreadsheet with an initial value for y when t=0 it'll produce the estimated values
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Aug 2008
    Posts
    27
    Ok for the backward one my tutor gave me this

    y=(y+dt e^(-n dt))/(1+20 dt)

    I don't understand how he's got that. Any ideas?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Feb 2009
    Posts
    4
    Well for a backwards step approach the equation just becomes:

    \mathsf{y_{i-1}=y_i-f(y_i,t_i)\cdot \Delta t} and needs an initial value for y when t=10.

    I'm not really sure what the n represents in that equation, I may have learnt the method with different notation to the way your tutor is teaching it.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Urgent!!!help with attempted questions - urgent
    Posted in the Statistics Forum
    Replies: 2
    Last Post: February 28th 2010, 01:29 AM
  2. I need urgent urgent hel with this parabola question
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: December 14th 2008, 05:48 PM
  3. Very urgent!
    Posted in the Algebra Forum
    Replies: 2
    Last Post: September 30th 2008, 02:01 PM
  4. Urgent HW help
    Posted in the Discrete Math Forum
    Replies: 2
    Last Post: March 14th 2008, 06:52 AM
  5. urgent HELP
    Posted in the Statistics Forum
    Replies: 1
    Last Post: July 12th 2007, 05:34 AM

Search Tags


/mathhelpforum @mathhelpforum