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Finding an approximate function for a PD...

Al86 145 Maple 2015
plot input
October 31 2015
1 8

Are there any commands in maple that will help me find a suitable function that approximates the numerical solution of:



> 

  restart;
  PDE := diff(v(x, t), t) = diff(v(x, t), x, x);
  JACOBIINTEGRAL := int(JacobiTheta3(0, exp(-Pi^2*s))*v(1, t-s)^4, s = 0 .. t);
  IBC:= D[1](v)(0,t)=0,
        D[1](v)(1,t)=-0.000065*v(1, t)^4,
        v(x,0)=1;
#
# For x=0..1, t=0..1, the solution varies only very slowly
# so I have increased the timestep/spacestep, just to speed
# up results generation for diagnostic purposes
#
  pds := pdsolve( PDE, [IBC], numeric, time = t, range = 0 .. 1,
                  spacestep = 0.1e-1, timestep = 0.1e-1,
                  errorest=true
                )

diff(v(x, t), t) = diff(diff(v(x, t), x), x)

  

int(JacobiTheta3(0, exp(-Pi^2*s))*v(1, t-s)^4, s = 0 .. t)

  

(D[1](v))(0, t) = 0, (D[1](v))(1, t) = -0.65e-4*v(1, t)^4, v(x, 0) = 1

  

_m649569600

 (1)
> 

#
# Plot the solution over the ranges x=0..1,
# time=0..1. Not a lot happens!
#
  pds:-plot(x=1, t=0..1);

 
> 

#
# Plot the estimated error over the ranges x=0..1,
# time=0..1
#
  pds:-plot( err(v(x,t)), x=1,t=0..1);

 
> 

#
# Get some numerical solution values
#
  pVal:=pds:-value(v(x,t), output=procedurelist):
  for k from 0 by 0.1 to 1 do
      pVal(1, k)[2], pVal(1, k)[3];
  od;
> 

 

t = 0., v(x, t) = Float(undefined)

  

t = .1, v(x, t) = .999977377613528229

  

t = .2, v(x, t) = .999967577518313666

  

t = .3, v(x, t) = .999959874331053822

  

t = .4, v(x, t) = .999952927885405241

  

t = .5, v(x, t) = .999946262964885979

  

t = .6, v(x, t) = .999939702966688881

  

t = .7, v(x, t) = .999933182128311282

  

t = .8, v(x, t) = .999926675964661227

  

t = .9, v(x, t) = .999920175361791563

  

t = 1.0, v(x, t) = .999913676928735229

 (2)
> 

 

> 

 

 

Download PDEprob2_(2).mw

 

I am refering to the first graph, is there a way in maple to find an explicit suitable approximating function?

I.e, I want the function to have the same first graph obviously, it seems like addition of exponent and a line function, I tried plotting exp(-t)-0.3*t, it doesn't look like it approximates it very well. Any suggestion on how to implement this task in maple?

Thanks.

 

Problem in plotting ...

Al86 145 Maple
plot pde
October 13 2015
1 18

I have the solution to a heat PDE, v and the error esitmate u + cos(x+t) = v

 

I want to plot log v(1,t) as function of log u(1,t) in maple, but I seem to get an error:

Error, (in plot) unexpected option: ln(u(1, t))

 

I am attaching my code below.

How to fix this problem?

Thanks in advance.

PDE+cos.mw

Solving a nonlinear hyperbolic PDE...

Al86 145 Maple 2015
pde pdsolve
September 04 2015
0 0

I am considering the following PDE and I am getting an error, please suggest a better numerical method than the default one used in maple:

 

the PDE is:

u_{xx}u^3 - sin(xt)u_{tt} = u(x,t)

u(x, 0) = sin(x), (D[2](u))(x, 0) = cos(x), u(0, t) = cos(t), (D[1](u))(0, t) = sin(t)

Please suggest me a method that will also work for the following PDEs:

u^m* u_{xx} - sin(xt)u_{tt} = u^n

for m,n =0,1,2,3,... for the cases m=n and m not equal n

Here's the code:

 

> 

pde := u(x, t)^3*(diff(u(x, t), x, x))-sin(x*t)*(diff(u(x, t), t, t)) = u(x, t);

u(x, t)^3*(diff(diff(u(x, t), x), x))-sin(x*t)*(diff(diff(u(x, t), t), t)) = u(x, t)

 (1)
> 

ibc := u(x, 0) = sin(x), (D[2](u))(x, 0) = cos(x), u(0, t) = cos(t), (D[1](u))(0, t) = sin(t);

u(x, 0) = sin(x), (D[2](u))(x, 0) = cos(x), u(0, t) = cos(t), (D[1](u))(0, t) = sin(t)

 (2)
> 

pds := pdsolve(pde, [ibc], numeric, time = t, range = 0 .. 1, spacestep = 0.1e-1)

module () local INFO; export plot, plot3d, animate, value, settings; option `Copyright (c) 2001 by Waterloo Maple Inc. All rights reserved.`; end module

 (3)
> 

pds:-plot3d(u(x, t), t = 0 .. 1, x = 0 .. 1, labels = [t, x, u(x, t)], labelfont = [times, bold, 20], axesfont = [times, bold, 16])

Error, (in pdsolve/numeric/plot3d) unable to compute solution for t>HFloat(0.0):
Newton iteration is not converging

  
> 

``

 

Download nonlinear_hyperbolic_PDE.mw

Wave PDE equation...

Al86 145 Maple
pde pdsolve
August 29 2015
1 0

I have the following PDE:

 

u_xx = u_tt + (2^{1/2}u_x-u)^{1/2}

 

Do you have a proposed algorithm to solve in maple for this PDE? I mean pdsolve won't solve it because it's a nonlinear PDE.

 

PDE to solve numerically...

Al86 145 Maple 2015
assumptions pde numeric
August 22 2015
1 9

I want to solve numerically the PDE:

u_xx + u_yy= = u^{1/2}+(u_x)^2/(u)^{3/2}

 

My assumptions are that  |sqrt(2)u_x/u|<<1 (but I cannot neglect the first term since its in my first order approximation of another PDE.

 

So I tried solving by using pdsolve in maple, but to no cigar.

 

Here's the maple file:

 nonlinear.mw

> 

PDE := diff(diff(u(x, y), x), x)+diff(diff(u(x, y), y), y) = u^(1/2)+(diff(u(x, y), x))^2/u^(3/2); IBC := {D[1](u)*(1, t) = 0, D[2](u)*(x, 1) = 0, u(0, t) = 1, u(x, 0) = 1}; pds := pdsolve(PDE, IBC, type = numeric); pds:-plot3d(t = 0 .. 1, x = 0 .. 1, axes = boxed, orientation = [-120, 40], color = [0, 0, u])

diff(diff(u(x, y), x), x)+diff(diff(u(x, y), y), y) = u^(1/2)+(diff(u(x, y), x))^2/u^(3/2)

  

{D[1](u)*(1, t) = 0, D[2](u)*(x, 1) = 0, u(0, t) = 1, u(x, 0) = 1}

  

Error, (in pdsolve/numeric/process_PDEs) all dependent variables in PDE must have dependencies explicitly declared, got {u}

  

Error, `pds` does not evaluate to a module

  
> 

``

 

Download nonlinear.mw

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