Re: [xAct] Writing a function to calculate the post-Newtonian order

[Thomas Bäckdahl]

Hi!

This depends a bit on how complicated expression you should be able to handle, but to handle some simple cases you could try:
PNOrder[r] = -1;
PNOrder[v] = 0.5;
PNOrder[c_?ConstantQ] := 0;
PNOrder[Power[a_, n_]] := n*PNOrder[a];
PNOrder[prod_Times] := Plus @@ (PNOrder /@ List @@ prod);

Regards
Thomas

On 2023-03-20 19:37, Aniket Khairnar wrote:

Hi,

       I am trying to write a function that can calculate the post-Newtonian order of an expression. But I don't know how to proceed. Here is what the function should do.

PNOrder[expr_] = 

given that,

PNOrder[r] = -1

PNOrder[v] = 0.5

The expr would be an algebraic combination of r and v. How to write such a function with these conditions?

For ex, it should give

PNOrder[r*v] = -0.5

Regards,

Aniket Khairnar

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