refactoring solver_cese.py: abandon variable dt
refactoring solver_cese.py: abandon variable dt

yungyuc/solvcon,solvcon/solvcon,solvcon/solvcon,solvcon/solvcon,solvcon/solvcon,solvcon/solvcon,yungyuc/solvcon,solvcon/solvcon,yungyuc/solvcon,yungyuc/solvcon,yungyuc/solvcon,yungyuc/solvcon