# Understand the meaning of & operator?

Posted 2 months ago
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 Hi there,A simple problem appeared and I can't solve it by myself. Plese don't focus on the meaning of the functions and of the values assigned to variables: I suspect the problem is on how I treat aa and bb.After defining the following functions XX and Hvv that I can call in the code: XX = -Inverse[aa].(bb.UU ); Hvv = cc.(Inverse[s i - aa].bb); If I call X=XX&[aa=4,bb=5,cc=6] and then call Hvv Hv=Hvv&[aa=6,bb=7] I get wrong values for Hv.But if after calling X=XX&(ecc.) I re-evaluate the definition of Hvv = cc.(Inverse[s i - aa].bb) then everything is fine if I call now Hv=Hvv(ecc.).I guess I'm misunderstanding the meaning of f(aa)&(aa=a) which I intend as "evaluate f ifor aa=a".You guys have insight on how to solve this? Thanks. Answer
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Posted 2 months ago
 Are you able to provide a minimal example with code one could actually evaluate? I think there are some fundamental issues in your syntax. For example to define a function XX with 3 arguments you would want to instead do XX[aa_, bb_, UU_] := -Inverse[aa].(bb.UU ) or something similar. The following doesn't really make a ton of sense: XX = -Inverse[aa].(bb.UU ); X=XX&[aa=4,bb=5,cc=6] Consider this documentation page: https://reference.wolfram.com/language/tutorial/DefiningFunctions.html Answer
Posted 2 months ago
 Thanks a lot. I'm learning Mathematica bit by bit so I do not have the general picture. Now I know how to define and call proper functions and the code works fine.What I did until know (and worked until now) was declaring variables (dependent "functions") which depended on other variables (independent variables) and then evaluate the dependent ones using & operator on the independent. Answer
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