John Fredsted

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19 years, 180 days

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These are questions asked by John Fredsted

Consider the following:

Setup(anticommutativeprefix = psi):
psi^2,psi__1^2,psi__a^2;   # double underscores

Why does the square of psi__a (double underscore) not vanish as well? Or, perhaps, more to the point: why is psi__a not as well considered Grassmann-odd by Maple? Is this counter-intuitive behaviour intentional, or is it a bug?

Moments ago, when I consulted the help pages, there popped up an Update window followed by a download of some 100MB+, and then nothing more seemed to happen. What was that about?, I wonder. Was it automatic updating of the help pages, or what?

To my amazement, the following code hangs

Setup(anticommutativeprefix = psi):

at the last line, or produces the output "Error, (in sprintf) too many levels of recursion" if I wait long enough.

What is going on? Am I just being stupid? The version line verifies to me that I am using the Physics package as shipped with Maple 2017, version date 17th of May 2017. If I outcomment the Setup line, then Dagger does not hang. Do others experience the same behaviour?

I am somewhat surprised to find that


say, returns 1. Does that really make mathematical sense with diff(f(x),x) here being the argument of a function?

PS: I bumped into this issue because I was trying to write down some structured type, or some other matching criterium, that will return true for some scalarly quantity consisting of any number of functions and their derivatives if and only if all arguments to all functions have differential order zero. This criterium would exclude the above function, for instance.

Update: Just for the sake of completeness, or as a service to any visitor to this thread, the above was readily resolved as being due to a blunder of mine, see a comment of mine below. The thread, though, developed into a quite interesting one concerning issues with conserved currents, and related, in the case of Grassmann-odd quantities, issues that are at the time of writing still unresolved.

The following construction of a simple vector of matrices (just a test example)

Vector(2,(a) -> Matrix(2,2,(b,c) -> m||a||b||c));

works in Maple 17, but not in Maple 2017 where the error message "Error, (in Vector[column]) number of elements on right side must match subselection on left side" is produced. Why that?

Update: If no output is prompted, i.e., if the above line is terminated with colon instead of semicolon, then no error is raised. What?!

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