Hi, I'm new to QSymm and I'm just running through the tutorials from readthedocs. It appears to me that whenever I try to convert a string hamiltonian with J>=1, it returns some error codes.  This is part of the tutorial code that I downloaded from the readthedocs. I've also tried to use J=1, but it returns a similar error: The details of the error codes are attached below: ``` --------------------------------------------------------------------------- ValueError Traceback (most recent call last) ValueError: Error from parse_expr with transformed code: "Symbol ('hbar' )**Integer (2 )/(Integer (2 )*Symbol ('m' ))*(k_x **Integer (2 )+k_y **Integer (2 )+k_z **Integer (2 ))*eye (Integer (4 ))+Symbol ('alpha' )*J_x *k_x +Symbol ('alpha' )*J_y *k_y +Symbol ('alpha' )*J_z *k_z " The above exception was the direct cause of the following exception: TypeError Traceback (most recent call last) <ipython-input-14-b84411f42ce9> in <module> 4 "alpha * J_x * k_x + alpha * J_y * k_y + alpha * J_z * k_z" 5 ) ----> 6 H_rashba = qsymm.Model(ham_rashba, locals=dict(J_x=J_x, J_y=J_y, J_z=J_z)) 7 H_rashba.tosympy(nsimplify=True) ~/opt/anaconda3/lib/python3.8/site-packages/qsymm/model.py in __init__(self, hamiltonian, locals, momenta, keep, symbol_normalizer, normalize, shape, format) 205 else: 206 # Try to parse the input with kwant_continuum.sympify --> 207 hamiltonian = kwant_continuum.sympify(hamiltonian, locals=locals) 208 if not isinstance(hamiltonian, MatrixBase): 209 hamiltonian = sympy.Matrix([[hamiltonian]]) ~/opt/anaconda3/lib/python3.8/site-packages/qsymm/kwant_continuum.py in sympify(expr, locals) 213 stored_value = converter.pop(list, None) 214 converter[list] = lambda x: sympy.Matrix(x) --> 215 hamiltonian = sympy.sympify(expr, locals=locals) 216 # if input is for example ``[[k_x * A(x) * k_x]]`` after the first 217 # sympify we are getting list of sympy objects, so we call sympify ~/opt/anaconda3/lib/python3.8/site-packages/sympy/core/sympify.py in sympify(a, locals, convert_xor, strict, rational, evaluate) 477 try: 478 a = a.replace('\n', '') --> 479 expr = parse_expr(a, local_dict=locals, transformations=transformations, evaluate=evaluate) 480 except (TokenError, SyntaxError) as exc: 481 raise SympifyError('could not parse %r' % a, exc) ~/opt/anaconda3/lib/python3.8/site-packages/sympy/parsing/sympy_parser.py in parse_expr(s, local_dict, transformations, global_dict, evaluate) 1016 return eval_expr(code, local_dict, global_dict) 1017 except Exception as e: -> 1018 raise e from ValueError(f"Error from parse_expr with transformed code: {code!r}") 1019 1020 ~/opt/anaconda3/lib/python3.8/site-packages/sympy/parsing/sympy_parser.py in parse_expr(s, local_dict, transformations, global_dict, evaluate) 1014 1015 try: -> 1016 return eval_expr(code, local_dict, global_dict) 1017 except Exception as e: 1018 raise e from ValueError(f"Error from parse_expr with transformed code: {code!r}") ~/opt/anaconda3/lib/python3.8/site-packages/sympy/parsing/sympy_parser.py in eval_expr(code, local_dict, global_dict) 908 Generally, ``parse_expr`` should be used. 909 """ --> 910 expr = eval( 911 code, global_dict, local_dict) # take local objects in preference 912 return expr <string> in <module> TypeError: unsupported operand type(s) for +: 'MutableDenseMatrix' and 'ImmutableDenseNDimArray' --------------------------------------------------------------------------- ValueError Traceback (most recent call last) ValueError: Error from parse_expr with transformed code: "Symbol ('hbar' )**Integer (2 )/(Integer (2 )*Symbol ('m' ))*(k_x **Integer (2 )+k_y **Integer (2 )+k_z **Integer (2 ))*eye (Integer (4 ))+Symbol ('alpha' )*J_x *k_x +Symbol ('alpha' )*J_y *k_y +Symbol ('alpha' )*J_z *k_z " The above exception was the direct cause of the following exception: TypeError Traceback (most recent call last) <ipython-input-14-b84411f42ce9> in <module> 4 "alpha * J_x * k_x + alpha * J_y * k_y + alpha * J_z * k_z" 5 ) ----> 6 H_rashba = qsymm.Model(ham_rashba, locals=dict(J_x=J_x, J_y=J_y, J_z=J_z)) 7 H_rashba.tosympy(nsimplify=True) ~/opt/anaconda3/lib/python3.8/site-packages/qsymm/model.py in __init__(self, hamiltonian, locals, momenta, keep, symbol_normalizer, normalize, shape, format) 205 else: 206 # Try to parse the input with kwant_continuum.sympify --> 207 hamiltonian = kwant_continuum.sympify(hamiltonian, locals=locals) 208 if not isinstance(hamiltonian, MatrixBase): 209 hamiltonian = sympy.Matrix([[hamiltonian]]) ~/opt/anaconda3/lib/python3.8/site-packages/qsymm/kwant_continuum.py in sympify(expr, locals) 213 stored_value = converter.pop(list, None) 214 converter[list] = lambda x: sympy.Matrix(x) --> 215 hamiltonian = sympy.sympify(expr, locals=locals) 216 # if input is for example ``[[k_x * A(x) * k_x]]`` after the first 217 # sympify we are getting list of sympy objects, so we call sympify ~/opt/anaconda3/lib/python3.8/site-packages/sympy/core/sympify.py in sympify(a, locals, convert_xor, strict, rational, evaluate) 477 try: 478 a = a.replace('\n', '') --> 479 expr = parse_expr(a, local_dict=locals, transformations=transformations, evaluate=evaluate) 480 except (TokenError, SyntaxError) as exc: 481 raise SympifyError('could not parse %r' % a, exc) ~/opt/anaconda3/lib/python3.8/site-packages/sympy/parsing/sympy_parser.py in parse_expr(s, local_dict, transformations, global_dict, evaluate) 1016 return eval_expr(code, local_dict, global_dict) 1017 except Exception as e: -> 1018 raise e from ValueError(f"Error from parse_expr with transformed code: {code!r}") 1019 1020 ~/opt/anaconda3/lib/python3.8/site-packages/sympy/parsing/sympy_parser.py in parse_expr(s, local_dict, transformations, global_dict, evaluate) 1014 1015 try: -> 1016 return eval_expr(code, local_dict, global_dict) 1017 except Exception as e: 1018 raise e from ValueError(f"Error from parse_expr with transformed code: {code!r}") ~/opt/anaconda3/lib/python3.8/site-packages/sympy/parsing/sympy_parser.py in eval_expr(code, local_dict, global_dict) 908 Generally, ``parse_expr`` should be used. 909 """ --> 910 expr = eval( 911 code, global_dict, local_dict) # take local objects in preference 912 return expr <string> in <module> TypeError: unsupported operand type(s) for +: 'MutableDenseMatrix' and 'ImmutableDenseNDimArray' ```