## a staged problem question

General discussions about how to formulate a script for FlexPDE.

### a staged problem question

Asking for help here, not asking for how to solve the problem. I keep getting this error message: "the evaluator has referenced an eigenvector but no node number has been specified".I thought I had this matter resolved but clearly, I have not. Please help me.

title 'Staged Problem'

select
stages = 4{ run only the first three of the listed stages }
errlim = staged(0.1, 0.01, 0.001, 0.0001)
rematrix=on !<=Jacobian
Variables
U Hz
definitions
scale = staged(1, 2, 4, 6) { extra value ignored }
a = 1/scale
epsilon= 0
dr(Hz) = (x/r)*dx(Hz) + (y/r)*dy(Hz) { functional definition of polar derivatives... }
dphi(Hz) = (-y)*dx(Hz) + x*dy(Hz) {... in cartesian coordinates }
wt=(stage-1)/pi
i=sqrt(-1)
Hz01 = 0.50*sin(pi*wt)
Hz02 = 0.50*sin(pi*wt+(epsilon))
source=Hz01+Hz02

Initial values
u =(1/cosh((x-a)/2)^2) Hz=0
equations
U: div(a*grad(u)) + scale*u*dx(u) +4 = 0; {is burger's equation}
Hz: r*dr(r*dr(Hz)) + dphi(dphi(Hz)) + r*r*lambda*Hz +r*r*source =0 {Eigenvalue Problem}
boundaries

region 1
start(29.7,0)
value(u)=0
arc(center=0,0) angle = 360
value(u) = sin(120*pi*(x+y))

Region 2
start (-12.5,10.0) line to (-10.5,10.0) arc(center=0,10) angle= -180 nobc(u)
start (12.5,10.0) value(u)=0 arc(center=0,10) angle= 180 line to close
start (-12.5,8.0) line to(-12.5, 24.0) value(u)=0 line to(-15.5,24.0) value(u)=0 line to(-15.5,8.0) close
start (12.5,8.0) line to(12.5, 24.0) value(u)=0 line to(15.5,24.0) value(u)=0 line to(15.5,8.0) close

monitors
contour(u)
surface(u)
plots
surface(u) report scale as "Scale"
contour(u) report scale as "Scale"

histories
history(integral(u)) vs scale as "Integral vs Scale"
end
compxci

Posts: 16
Joined: Tue Oct 25, 2011 7:18 pm

### Re: a staged problem question

FlexPDE does not currently have provision for solving nonlinear eigenvalue problems.
There is an oversight in the diagnostic process that detects and reports this, so that the error report is a confusing one (although it identifies the offending term).
In the next release, we will fix the diagnostic to be more informative, but the core restriction of eigenvalue problems to linear equation systems remains.
moderator

Posts: 362
Joined: Tue Jan 11, 2011 1:45 pm