[Example] Fix the ti example problems of sparse matrix demos (#3215)

* a quick solve

* fix mass spring

* remove sys

* add todo and issue

* fix typo

examples/simulation/implicit_mass_spring.py

@@ -233,7 +233,7 @@ def displayGGUI(self, canvas, radius=0.01, color=(1.0, 1.0, 1.0)):
                         '--use-ggui',
                         action='store_true',
                         help='Display with GGUI')
-    args = parser.parse_args()
+    args, unknowns = parser.parse_known_args()
     use_ggui = False
     use_ggui = args.use_ggui
 

examples/simulation/stable_fluid.py

@@ -12,13 +12,13 @@
 
 # How to run:
 #   `python stable_fluid.py`: use the jacobi iteration to solve the linear system.
-#   `python stable_fluid.py -s`: use a sparse matrix to do so.
+#   `python stable_fluid.py -S`: use a sparse matrix to do so.
 parser = argparse.ArgumentParser()
-parser.add_argument('-s',
+parser.add_argument('-S',
                     '--use-sp-mat',
                     action='store_true',
                     help='Solve Poisson\'s equation by using a sparse matrix')
-args = parser.parse_args()
+args, unknowns = parser.parse_known_args()
 
 res = 512
 dt = 0.03

python/taichi/main.py

@@ -180,6 +180,8 @@ def example(self, arguments: list = sys.argv[2:]):
             dest='save',
             action='store_true',
             help="Save source code to current directory instead of running it")
+
+        # TODO: Pass the arguments to downstream correctly(#3216).
         args = parser.parse_args(arguments)
 
         examples_dir = TaichiMain._get_examples_dir()