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Re: matrix operations -- shared data vs copied


B=A copies A, it doesn't link to A changing A after this statement
doesn't change B

otherwise, this would be invalid input:
a = 1
a = a + 1

You seem to be using a model of thinking about Mathematica that doesn't
really mesh with the way it operates.

B=A is really just like a rule B->A that is always active whenever the
evaluator finds an expression with B in it

B:=A, while it might be tempting to think of as a "link" from B to A,
is really a delayed rule B:>A that is always active whenever the
evaluator finds an expression with B in it

The difference between the two, = and :=, comes into play with patterns
and with the state of A when B is encountered.

If you don't want to read the Mathematica Book one billion times, I
suggest paying someone to instruct you on how to use Mathematica - that
way, you'll only have to read the Mathematica book one million times.
Maybe try Mathematica classes??


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