I am having trouble understanding what is going wrong when trying to use the Coefficient function on expressions in InputForm. A very simple example serves to illustrate.
In[1]:= a = 3 x + 4 y // InputForm
Out[1]//InputForm=
3*x + 4*y
In[2]:= Coefficient[a, x]
Out[2]= 0
Is there any way to make this work, or convert the old expression back into Standard form? Cheers!
We can use FullForm to see what a really is, as
a = 3 x + 4 y // InputForm
a // FullForm
(* InputForm[Plus[Times[3,x],Times[4,y]]] *)
We see that a has the head InputForm. What we want to pass to Coefficient is the expression that has the head Plus. We can do that with
Coefficient[a//First,x]
(* 3 *)
Do we really need the head of a to be InputForm? If not, we could use parentheses like this
(a = 3 x + 4 y) // InputForm
(* 3*x + 4*y *)
Coefficient[a,x]
(* 3 *)
...Formwrappers the way you might expect (i.e. by simply ignoring them). If you look at theFullFormofa, you'll see that everything is wrapped insideInputForm. And an expression of the formInputForm[...]has coeffient0forx, so the result you're getting is technically correct $\endgroup$