Merge pull request #1730 from SciML/myb/sparsity

Better error msg and set the size of the sparsity matrix

Author: YingboMa

src/structural_transformation/codegen.jl

@@ -93,7 +93,7 @@ function torn_system_with_nlsolve_jacobian_sparsity(state, var_eq_matching, var_
             end
         end
     end
-    sparse(I, J, true)
+    sparse(I, J, true, length(eqs_idxs), length(states_idxs))
 end
 
 function gen_nlsolve!(is_not_prepended_assignment, eqs, vars, u0map::AbstractDict,

src/systems/diffeqs/odesystem.jl

@@ -333,7 +333,7 @@ function build_explicit_observed_function(sys, ts;
             eqs_dict = eqs_cache[]
             rhs = get(eqs_dict, v, nothing)
             if rhs === nothing
-                error("Observed variables depends on differentiated variable $v, but it's not explicit solved. Fix file an issue if you are sure that the system is valid.")
+                error("The observed variable $(eq.lhs) depends on the differentiated variable $v, but it's not explicit solved. Fix file an issue if you are sure that the system is valid.")
             end
         end
         empty!(vars)