In the following session I create several symbolic expressions and
manipulate them via substitution.
Why does the last command produce an error?
Jupyter console 5.0.0
Python 3.5.2 (v3.5.2:4def2a2901a5, Jun 25 2016, 22:01:18) [MSC v.1900 32
bit (Intel)]
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IPython 5.1.0 -- An enhanced Interactive Python.
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help -> Python's own help system.
object? -> Details about 'object', use 'object??' for extra details.
In [1]: import sympy
In [2]: sympy.__version__
Out[2]: '1.0'
In [3]: sympy.var('Xa,Ya,Za,Xb,Yb,Zb,Na,Nb,Sa,Sb')
Out[3]: (Xa, Ya, Za, Xb, Yb, Zb, Na, Nb, Sa, Sb)
In [4]: Sa=Xa/7
In [5]: Sb=Yb**3
In [6]: Sa - Sb
Out[6]: Xa/7 - Yb**3
In [7]: NEa=sympy.Matrix([[Xa,Ya,Za]])
In [8]: NEb=sympy.Matrix([[Xb,Yb,Zb]])
In [9]: NEa - NEb
Out[9]: Matrix([[Xa - Xb, Ya - Yb, Za - Zb]])
In [10]: V=Na-Nb
In [11]: V.subs({Na:Sa,Nb:Sb})
Out[11]: Xa/7 - Yb**3
In [12]: V.subs({Na:NEa,Nb:NEb})
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
Long Traceback output follows ending with
AttributeError: ImmutableMatrix has no attribute as_coeff_Mul.
Which I don't understand in any useful way.
What concept am I missing? Are matrices not substitutable?
NT
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