diff and pdiff method of class Mv throws exception when differentiate by a coordinate symbol

[mammalwong]

x is a coordinate symbol (a plain sympy Symbol object) and ex is a Mv instance of a Ga basis symbol. I tried to invoke (x*ex).diff(x) and the method throws exception. From the exception stack frame below, it looks like Mv.diff passed self.obj to Ga.pDiff and pDiff try to resolve .obj again from obj.

---

AttributeError Traceback (most recent call last)
in <cell line: 1>()
----> 1 (x*ex).diff(x)

1 frames
/usr/local/lib/python3.10/dist-packages/galgebra/mv.py in diff(self, coord)
1070 obj += tmp1 * tmp2
1071 else:
-> 1072 obj = self.Ga.pDiff(self.obj, coord)
1073 return Mv(obj, ga=self.Ga)
1074

/usr/local/lib/python3.10/dist-packages/galgebra/ga.py in pDiff(self, A, coord)
2050 # variable, but including case of non-constant basis vectors
2051
-> 2052 dA = self.mv(expand(diff(A.obj, coord)))
2053
2054 if self.connect_flg and self.dslot == -1 and not A.is_scalar(): # Basis blades are function of coordinates

AttributeError: 'Mul' object has no attribute 'obj'

[mammalwong]

pdiff method of Mv class also throws the same exception when invoking (x*ex).pdiff(x).

---

AttributeError Traceback (most recent call last)
in <cell line: 1>()
----> 1 (x*ex).pdiff(x)

1 frames
/usr/local/lib/python3.10/dist-packages/galgebra/ga.py in pDiff(self, A, coord)
2050 # variable, but including case of non-constant basis vectors
2051
-> 2052 dA = self.mv(expand(diff(A.obj, coord)))
2053
2054 if self.connect_flg and self.dslot == -1 and not A.is_scalar(): # Basis blades are function of coordinates

AttributeError: 'Mul' object has no attribute 'obj'

[utensil]

@mammalwong Can you also post minimal working example for this issue? Thanks!

[mammalwong]

In version 0.5.1

x,y,z = coords = S.symbols('x y z', real=True)
ga = Ga('e', g=[1,1,1], coords=coords, wedge=False)
ex,ey,ez = ga.mv()
(x*ex).diff(x)

raise exception:

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
[<ipython-input-9-4979ad157f80>](https://localhost:8080/#) in <cell line: 4>()
      2 ga = Ga('e', g=[1,1,1], coords=coords, wedge=False)
      3 ex,ey,ez = ga.mv()
----> 4 (x*ex).diff(x)

1 frames
[/usr/local/lib/python3.10/dist-packages/galgebra/mv.py](https://localhost:8080/#) in diff(self, coord)
   1070                         obj += tmp1 * tmp2
   1071         else:
-> 1072             obj = self.Ga.pDiff(self.obj, coord)
   1073         return Mv(obj, ga=self.Ga)
   1074 

[/usr/local/lib/python3.10/dist-packages/galgebra/ga.py](https://localhost:8080/#) in pDiff(self, A, coord)
   2050         # variable, but including case of non-constant basis vectors
   2051 
-> 2052         dA = self.mv(expand(diff(A.obj, coord)))
   2053 
   2054         if self.connect_flg and self.dslot == -1 and not A.is_scalar():  # Basis blades are function of coordinates

AttributeError: 'Mul' object has no attribute 'obj'

---

Another related issue:

x,y,z = coords = S.symbols('x y z', real=True)
ga = Ga('e', g=[1,1,1], coords=coords, wedge=False)
ex,ey,ez = ga.mv()
(x*ex).pdiff(x) # notice this is pdiff() not diff() this time

raise exception:

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
[<ipython-input-10-5767979f98eb>](https://localhost:8080/#) in <cell line: 4>()
      2 ga = Ga('e', g=[1,1,1], coords=coords, wedge=False)
      3 ex,ey,ez = ga.mv()
----> 4 (x*ex).pdiff(x)

1 frames
[/usr/local/lib/python3.10/dist-packages/galgebra/mv.py](https://localhost:8080/#) in pdiff(self, var)
   1074 
   1075     def pdiff(self, var) -> 'Mv':
-> 1076         return Mv(self.Ga.pDiff(self.obj, var), ga=self.Ga)
   1077 
   1078     def Grad(self, coords, mode: str = '*', left: bool = True) -> 'Mv':

[/usr/local/lib/python3.10/dist-packages/galgebra/ga.py](https://localhost:8080/#) in pDiff(self, A, coord)
   2050         # variable, but including case of non-constant basis vectors
   2051 
-> 2052         dA = self.mv(expand(diff(A.obj, coord)))
   2053 
   2054         if self.connect_flg and self.dslot == -1 and not A.is_scalar():  # Basis blades are function of coordinates

AttributeError: 'Mul' object has no attribute 'obj'

[utensil]

Thank you, @mammalwong , the fix should be in master now as #510 is now merged.