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HW4 - it.uu.se · PDE2012$ ProblemSet$4$ $ $ Handin$nolaterthan$October24$ $...

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PDE 2012 Problem Set 4 Hand in no later than October 24 Consider the IBVP on domain 0≤x≤1, 0≤t for ! ! + ! ! = 0, ! ! ! ! = 0, with initial conditions ! ! , 0 = ! ! ! , ! ! , 0 = ! ! ! , and boundary conditions (a) or (b): ! ! 0, ! ! ! 0, ! = ! ! ! , ! 1, ! ! ! 1, ! = ! ! ! , ! ! 0, ! ! ! 0, ! = ! ! ! , ! 1, ! ! ! 1, ! = ! ! ! . 1. Investigate illposedness by looking for solutions e st with s=x+iy, x=Re(s)>0 of the corresponding problem with homogeneous boundary conditions. Show that one of the sets, (a) or (b), results in an illposed problem. Hint: you may investigate the determinant condition numerically. 2. Consider homogeneous initial data. For the other set of boundary conditions, show an estimate of the Laplace transformed solution in terms of the inhomogeneaus boundary functions. For which s is the estimate is valid? 3. Transform the estimate to physical space using ! !!!" !(, ! ) ! ! ! !" = ! !! ! (, ! + !" ) ! ! !! !"
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Page 1: HW4 - it.uu.se · PDE2012$ ProblemSet$4$ $ $ Handin$nolaterthan$October24$ $ Considerthe$IBVP$on$domain$0≤x≤1,0≤tfor$!=0,!$!=0,$ withinitialconditions$$!!!,0=!!!, !!,0 ...

PDE  2012  Problem  Set  4       Hand  in  no  later  than  October  24    

Consider  the  IBVP  on  domain  0≤x≤1,  0≤t  for  !! + !! = 0,    !! −  !! = 0,  

with  initial  conditions      ! !, 0 = !! ! , ! !, 0 = !! ! ,  

and  boundary  conditions  (a)  or  (b):  !        ! 0, ! − !! 0, ! = !! ! ,

! 1, ! − !! 1, ! = !! ! ,  !        ! 0, ! − !! 0, ! = !! ! ,

! 1, ! − !! 1, ! = !! ! .  1. Investigate  ill-­‐posedness  by  looking  for  solutions  est    with  s=x+iy,  x=Re(s)>0  of  the  corresponding  problem  with  homogeneous  boundary  conditions.  Show  that  one  of  the  sets,  (a)  or  (b),  results  in  an  ill-­‐posed  problem.  Hint:  you  may  investigate  the  determinant  condition  numerically.    

2. Consider  homogeneous  initial  data.  For  the  other  set  of  boundary  conditions,  show    an  estimate  of  the  Laplace  transformed  solution  in  terms  of  the  inhomogeneaus  boundary  functions.  For  which  s  is  the  estimate  is  valid?  

3. Transform  the  estimate  to  physical  space  using     !!!!" !(∙, !) !!! !" = !

!! !(∙, ! + !") !!!! !"  

   

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