uhh, column based indexing...

Author: ChrisRackauckas

src/integrators/rosenbrock_integrators.jl

@@ -52,7 +52,7 @@ end
         Calculus.finite_difference_jacobian!(uf,vec(uprev),vec(du1),J,integrator.alg.diff_type)
       end
     end
-    for i in 1:length(u), j in 1:length(u)
+    for j in 1:length(u), i in 1:length(u)
         @inbounds W[i,j] = @muladd mass_matrix[i,j]-γ*J[i,j]
     end
     integrator.alg.linsolve(vectmp,W,linsolve_tmp_vec,true)
@@ -163,7 +163,7 @@ end#
         Calculus.finite_difference_jacobian!(uf,vec(uprev),vec(du1),J,integrator.alg.diff_type)
       end
     end
-    for i in 1:length(u), j in 1:length(u)
+    for j in 1:length(u), i in 1:length(u)
         @inbounds W[i,j] = @muladd mass_matrix[i,j]-γ*J[i,j]
     end
     integrator.alg.linsolve(vectmp,W,linsolve_tmp_vec,true)