Solving an ODE using Galerkin's method

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SUMMARY

The discussion focuses on solving the ordinary differential equation (ODE) \(\frac{df}{dt}=f\) with the boundary condition \(f(0)=1\) using Galerkin's method. An approximate solution is proposed as \(f_{a}=1+\sum ^{3}_{k=1} a_{k}t^k\) for \(0\leq t\leq1\). Participants clarify that by differentiating the approximate solution and substituting it back into the ODE, one can derive three equations to solve for the coefficients \(a_{1}, a_{2}, a_{3}\). The discussion also highlights the challenge of non-orthogonal basis functions within the specified interval.

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  • Understanding of ordinary differential equations (ODEs)
  • Familiarity with Galerkin's method for approximating solutions
  • Basic knowledge of polynomial functions and their derivatives
  • Concept of boundary conditions in differential equations
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  • Explore the implications of non-orthogonal basis functions in numerical methods
  • Learn how to derive coefficients from polynomial approximations
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Homework Statement


Given the ODE [tex]\frac{df}{dt}=f[/tex] and the boundary condition [tex]f(0)=1[/tex]

One approximate solution is [tex]f_{a}=1+\sum ^{3}_{k=1} a_{k}t^k[/tex] where [tex]0\leq t\leq1[/tex]

Using the Galerkin's method find the coeficents [tex]a_{k}[/tex]

Homework Equations





The Attempt at a Solution


I don't think I've understood how to use the method really. So if someone could explain it briefly. Another thing that is mentioned in the book is that the basis funktions are not orthogonal on this interval. So that can not be imposed

Thanks
/Simon
 
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You can take the derivative of the general (approximate) solution and plug in the equation.
Then equate the terms with the same power of t and you'll get 3 simple equations that will give you the three coefficients a1, a2, a3.
 

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