Merge pull request #2493 from oscardssmith/os/fix-initdt

fix initdt calculation

Author: ChrisRackauckas

lib/OrdinaryDiffEqCore/src/initdt.jl

@@ -8,8 +8,8 @@
     oneunit_tType = oneunit(_tType)
     dtmax_tdir = tdir * dtmax
 
-    dtmin = nextfloat(integrator.opts.dtmin)
-    smalldt = convert(_tType, oneunit_tType * 1 // 10^(6))
+    dtmin = nextfloat(max(integrator.opts.dtmin, eps(t)))
+    smalldt = max(dtmin, convert(_tType, oneunit_tType * 1 // 10^(6)))
 
     if integrator.isdae
         return tdir * max(smalldt, dtmin)
@@ -235,8 +235,8 @@ end
     oneunit_tType = oneunit(_tType)
     dtmax_tdir = tdir * dtmax
 
-    dtmin = nextfloat(integrator.opts.dtmin)
-    smalldt = convert(_tType, oneunit_tType * 1 // 10^(6))
+    dtmin = nextfloat(max(integrator.opts.dtmin, eps(t)))
+    smalldt = max(dtmin, convert(_tType, oneunit_tType * 1 // 10^(6)))
 
     if integrator.isdae
         return tdir * max(smalldt, dtmin)

test/interface/ode_initdt_tests.jl

@@ -64,3 +64,9 @@ sol = solve(prob, Rodas5())
 # test that dtmin is set based on timespan
 prob = ODEProblem((u, p, t) -> 1e20 * sin(1e20 * t), 0.1, (0, 1e-19))
 @test solve(prob, Tsit5()).retcode == ReturnCode.Success
+
+#test that we are robust to u0=0, t0!=0
+integ = init(ODEProblem(((u,p,t)->u), 0f0, (20f0, 0f0)), Tsit5())
+@test abs(integ.dt) > eps(integ.t)
+integ = init(ODEProblem(((du,u,p,t)->du.=u), [0f0], (20f0, 0f0)), Tsit5())
+@test abs(integ.dt) > eps(integ.t)