15 May
2018
15 May
'18
12:01 p.m.
On 15 May 2018, at 11:49, Onno Bokhove <O.Bokhove@leeds.ac.uk> wrote:
HI David and Stephan,
Thanks.
Per the below: (i) The expression is a^1.5 but was written as a*sqrt(a); now that is corrected the nonlinear solver seems to work fine; apparently that rewrite matters for the Newton iteration.
The Jacobian is computed by automatic differentiation, so although mathematically a^1.5 and a*sqrt(a) are the same, they are differentiated differently to: 1.5 a^0.5 or 0.5 a / sqrt(a) + sqrt(a) The latter has a numerical singularity at 0. In floating point, if a is zero, you compute 0.0 / 0.0 => NaN Lawrence