move stats here as DEStats

src/solutions/ode_solutions.jl

@@ -1,6 +1,79 @@
 """
 $(TYPEDEF)
 
+Statistics from the differential equation solver about the solution process.
+
+## Fields
+
+- nf: Number of function evaluations. If the differential equation is a split function,
+  such as a `SplitFunction` for implicit-explicit (IMEX) integration, then `nf` is the
+  number of function evaluations for the first function (the implicit function)
+- nf2: If the differential equation is a split function, such as a `SplitFunction`
+  for implicit-explicit (IMEX) integration, then `nf2` is the number of function
+  evaluations for the second function, i.e. the function treated explicitly. Otherwise
+  it is zero.
+- nw: The number of W=I-gamma*J (or W=I/gamma-J) matrices constructed during the solving
+  process.
+- nsolve: The number of linear solves `W\b` required for the integration.
+- njacs: Number of Jacobians calculated during the integration.
+- nnonliniter: Total number of iterations for the nonlinear solvers.
+- nnonlinconvfail: Number of nonlinear solver convergence failures.
+- ncondition: Number of calls to the condition function for callbacks.
+- naccept: Number of accepted steps.
+- nreject: Number of rejected steps.
+- maxeig: Maximum eigenvalue over the solution. This is only computed if the
+  method is an auto-switching algorithm.
+"""
+mutable struct DEStats
+    nf::Int
+    nf2::Int
+    nw::Int
+    nsolve::Int
+    njacs::Int
+    nnonliniter::Int
+    nnonlinconvfail::Int
+    ncondition::Int
+    naccept::Int
+    nreject::Int
+    maxeig::Float64
+end
+
+DEStats(x::Int = -1) = DEStats(x, x, x, x, x, x, x, x, x, x, 0.0)
+
+function Base.show(io::IO, s::DEStats)
+    println(io, summary(s))
+    @printf io "%-50s %-d\n" "Number of function 1 evaluations:" s.nf
+    @printf io "%-50s %-d\n" "Number of function 2 evaluations:" s.nf2
+    @printf io "%-50s %-d\n" "Number of W matrix evaluations:" s.nw
+    @printf io "%-50s %-d\n" "Number of linear solves:" s.nsolve
+    @printf io "%-50s %-d\n" "Number of Jacobians created:" s.njacs
+    @printf io "%-50s %-d\n" "Number of nonlinear solver iterations:" s.nnonliniter
+    @printf io "%-50s %-d\n" "Number of nonlinear solver convergence failures:" s.nnonlinconvfail
+    @printf io "%-50s %-d\n" "Number of rootfind condition calls:" s.ncondition
+    @printf io "%-50s %-d\n" "Number of accepted steps:" s.naccept
+    @printf io "%-50s %-d" "Number of rejected steps:" s.nreject
+    iszero(s.maxeig) || @printf io "\n%-50s %-d" "Maximum eigenvalue recorded:" s.maxeig
+end
+
+function Base.merge(a::DEStats, b::DEStats)
+    DEStats(
+        a.nf + b.nf,
+        a.nf2 + b.nf2,
+        a.nw + b.nw,
+        a.nsolve + b.nsolve,
+        a.njacs + b.njacs,
+        a.nnonliniter + b.nnonliniter,
+        a.nnonlinconvfail + b.nnonlinconvfail,
+        a.ncondition + b.ncondition,
+        a.naccept + b.naccept,
+        a.nreject + b.nreject,
+        max(a.maxeig, b.maxeig),
+    ) 
+end
+
+"""
+$(TYPEDEF)
+
 Representation of the solution to an ordinary differential equation defined by an ODEProblem.
 
 ## DESolution Interface