Fixedpoint returns wrong result

[bertschi]

Hi,

consider the following function: f(x, p) = p .* x

When I solve for a fixed point everything works fine when p != 0. But when p = 0, the call fixedpoint(x -> f(x, 0.), [1.2]) just returns the initial condition, e.g. 1.2, and not the fixed point of zero. This also occurs when setting m = 0 which according to the documentation just gives Picard iteration. Don't understand how this could possibly fail. Any ideas?

Nils

[pkofod]

Can you show me the output? I get the correct answer.

[pkofod]

I'm seeing some test noise wrt fixedpoints so I'm looking into it.

[bertschi]

Your right, it works in version 4.2.0

julia> fixedpoint(x -> f(x, 0.), [1.2]) Results of Nonlinear Solver Algorithm

• Algorithm: Anderson m=1 beta=1 aa_start=1 droptol=0
• Starting Point: [1.2]
• Zero: [0.0]
• Inf-norm of residuals: 0.000000
• Iterations: 2
• Convergence: true
  • |x - x'| < 0.0e+00: true
  • |f(x)| < 1.0e-08: true
• Function Calls (f): 2
• Jacobian Calls (df/dx): 0

With version 4.0.0 instead, I get

fixedpoint(x -> f(x, 0.), [1.2]) Results of Nonlinear Solver Algorithm

• Algorithm: Anderson m=5 beta=1.0
• Starting Point: [1.2]
• Zero: [1.2]
• Inf-norm of residuals: 1.200000
• Iterations: 1
• Convergence: true
  • |x - x'| < 0.0e+00: true
  • |f(x)| < 1.0e-08: false
• Function Calls (f): 1
• Jacobian Calls (df/dx): 0

In any case, I was running on Julia 1.3.0. Will upgrade my dependencies which hopefully also solves the issue with my larger model.

[pkofod]

Fingers crossed :)

[pkofod]

I think this solved your bug https://github.com/JuliaNLSolvers/NLsolve.jl/commit/9b4c7b37e6fd2911d1fab77ebeabd450a039712b