the values in the still to be determined solution vector prior to the solution process act as the initial guess. you could populate the vector randomly if you so desired.
have a look at tut 21: "Before we solve for the pressure during a time step, we don't reset the solution variable to zero. The pressure (and the other variables) therefore have the previous time step's values at the time we get into the CG solver. Since the velocities and pressures don't change very much as computations progress, the previous time step's pressure is actually a good initial guess for this time step's pressure. Consequently, the number of iterations we need once we have computed the pressure once is significantly reduced." Andrew On 25 Jun 2010, at 5:16 PM, Satyendra Tomar wrote: > Hi everyone, > > I presume that the CG solver is taking the initial guess to be a zero > vector. Could someone please let me know how to change it to a random > vector? > > Bests, > Satyendra > PS: I haven't received any response to my previous post (Subject: > Timings of the mixed method for Poisson problem). I'm not sure if it > was successfully delivered (though I received a copy of that). > _______________________________________________ > dealii mailing list http://poisson.dealii.org/mailman/listinfo/dealii
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