Good luck with it. Cheers. On Wed, Jan 4, 2012 at 10:37 PM, Yun Tao <[email protected]> wrote:
> Never mind my last question. :P Having finally understood more about the > stochastic variable modules, the problem is revealed to be quite trivial. > > Thanks for the help! > > Happy 2012! > > On Wed, Jan 4, 2012 at 4:45 PM, Yun Tao <[email protected]> wrote: > >> Hi Daniel, >> >> What you wrote definitely guided me to the answer. Much thanks! SDE is >> actually just a PDE with its variable (and initial condition) being in the >> form of a probability distribution. On 1D mesh at least, fipy seems fully >> capable of handling that. >> >> On a slightly different note, your lucid explanation of noise variable >> (as second degree stochasticity) got me working through the examples in >> those links. Particularly, in >> < >> http://www.ctcms.nist.gov/fipy/fipy/generated/variables.html#module-fipy.variables.exponentialNoiseVariable >> > >> I may have spotted an error in the module: >> >> In short, I noticed that if the mean is set to Variable() -- defaulted to >> be 0 -- the encapsulating noise variable ("noise" in the example) will >> generate a *ValueError: scale <= 0* when called upon. Subsequently, >> feeding it into the viewer will yield >> * >> SystemError*: error return without exception set >> WARNING: Failure executing file: <enoise.py> >> >> A look at the exponential equation supports the condition of mean != 0. >> So does this mean the default mean for ExponentialNoiseVariable is poorly >> set and requires manual configuration for all future operations? >> >> Thanks! >> >> >> >> >> >> >> >> On Wed, Jan 4, 2012 at 8:16 AM, Daniel Wheeler <[email protected] >> > wrote: >> >>> >>> >>> On Tue, Jan 3, 2012 at 2:59 PM, Yun Tao <[email protected]> wrote: >>> >>>> Hi all, >>>> >>>> Having just jumped on the Fipy bandwagon, I'm wondering how it fares in >>>> handling stochastic PDEs. >>>> >>> >>> I don't know a whole lot about stochastic PDEs. We do have some examples >>> buried in doctests. See the examples in the following: >>> >>> < >>> http://www.ctcms.nist.gov/fipy/fipy/generated/variables.html#module-fipy.variables.uniformNoiseVariable >>> > >>> < >>> http://www.ctcms.nist.gov/fipy/fipy/generated/variables.html#module-fipy.variables.gammaNoiseVariable >>> > >>> < >>> http://www.ctcms.nist.gov/fipy/fipy/generated/variables.html#module-fipy.variables.exponentialNoiseVariable >>> > >>> < >>> http://www.ctcms.nist.gov/fipy/fipy/generated/variables.html#module-fipy.variables.exponentialNoiseVariable >>> > >>> < >>> http://www.ctcms.nist.gov/fipy/fipy/generated/variables.html#module-fipy.variables.gaussianNoiseVariable >>> > >>> < >>> http://www.ctcms.nist.gov/fipy/fipy/generated/variables.html#module-fipy.variables.betaNoiseVariable >>> > >>> >>> None of these include examples that actually solve a PDE, but the noise >>> variables can be tagged onto terms in the same way as other variables to >>> form PDEs that include stochastic sources. >>> >>> Having gone through multiple examples provided on the website so far, >>>> one of the major problems I'm facing is the setting of initial condition as >>>> a probability density function. This step seems to require more than just >>>> setting the value of CellVariable as a function of >>>> mesh.getCellCenters()[0]. Any insight? >>>> >>> >>> Would this do for a uniform mesh (for non-uniform meshes you can use the >>> the noise variables included above)? >>> >>> from fipy import Grid1D, CellVariable, numerix, Viewer >>> m = Grid1D(nx=100) >>> v = CellVariable(mesh=m) >>> v[:] = numerix.random.exponential(size=len(v)) >>> Viewer(v).plot() >>> raw_input('wait') >>> >>> Hope that helps. >>> >>> -- >>> Daniel Wheeler >>> >>> _______________________________________________ >>> fipy mailing list >>> [email protected] >>> http://www.ctcms.nist.gov/fipy >>> [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ] >>> >>> >> >> >> -- >> Yun Tao >> >> Graduate Group of Ecology Doctoral Candidate >> Department of Environmental Science and Policy >> Center for Population Biology >> University of California, Davis >> >> >> > > > -- > Yun Tao > > Graduate Group of Ecology Doctoral Candidate > Department of Environmental Science and Policy > Center for Population Biology > University of California, Davis > > > > _______________________________________________ > fipy mailing list > [email protected] > http://www.ctcms.nist.gov/fipy > [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ] > > -- Daniel Wheeler
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