Fix nonlinear problem instantiation

Author: YingboMa

src/systems/nonlinear/nonlinearsystem.jl

@@ -175,7 +175,7 @@ function DiffEqBase.NonlinearFunction{iip}(sys::NonlinearSystem, dvs = states(sy
 
     NonlinearFunction{iip}(f,
                      jac = _jac === nothing ? nothing : _jac,
-                     jac_prototype = sparse ? similar(sys.jac[],Float64) : nothing,
+                     jac_prototype = sparse ? similar(calculate_jacobian(sys, sparse=sparse),Float64) : nothing,
                      syms = Symbol.(states(sys)), observed = observedfun)
 end
 

test/nonlinearsystem.jl

@@ -124,14 +124,14 @@ np = NonlinearProblem(ns, [0,0,0], [1,2,3], jac=true, sparse=true)
        function makesys(name)
            @parameters a
            @variables x f
-   
+
            NonlinearSystem([0 ~ -a*x + f],[x,f],[a], name=name)
        end
-   
+
        function issue819()
            sys1 = makesys(:sys1)
            sys2 = makesys(:sys1)
            @test_throws ArgumentError NonlinearSystem([sys2.f ~ sys1.x, sys1.f ~ 0],[],[], systems=[sys1, sys2])
        end
        issue819()
-end
+end