# Is adjoint_inc_timestep neccessary for a repeated matrix-vector solve.

Asked by Gabriel Balaban

When the script below is run the replay_dolfin() function fails, but if the time-stepping information is added then the replay works! Doing the same thing with a series of variational problem solves without the timestepping information is ok as well. Is there something special about the matrix vector solves that requires them to always need time-stepping information?

from dolfin import *
from dolfin_adjoint import *

mesh = UnitSquareMesh(4,4)
V = FunctionSpace(mesh, "CG", 1)

u = TrialFunction(V)
v = TestFunction(V)

a = inner(grad(u), grad(v))*dx
u = Function(V, name = "solution")

bc = DirichletBC(V, 0, "on_boundary")

source = Expression("t*sin(x[0])*sin(x[1])", t = 0.0)
f = source*v*dx

t = 0.0
dt = 0.1

A = assemble(a)
#adj_start_timestep()
for i in range(2):
t += dt
source.t = t
F = assemble(f)
bc.apply(A)
bc.apply(F)
solve(A, u.vector(), F, "cg", "ilu")
#adj_inc_timestep(t)

adj_html("forward.html", "forward")
assert(replay_dolfin())

## Question information

Language:
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Status:
Answered
For:
dolfin-adjoint Edit question
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Last reply:
 Revision history for this message Patrick Farrell (pefarrell) said on 2013-06-14: #1

This is definitely a bug. I'll take a look at it now.

 Revision history for this message Gabriel Balaban (gabrib) said on 2013-06-14: #2

Thanks Patrick! It looks innocent at the moment but it's good know that you are checking to see if there is anything more to this.

 Revision history for this message Patrick Farrell (pefarrell) said on 2013-06-14: #3

That bug is now fixed in r726.

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