10.9.3 Can you answer these questions?

10.9.3.1 How to effectively substitute variables in xAct?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=300785

I am trying to find the gauge field equation by varying the Born-Infeld Action with the help of  xact  package. I use the following ... 
[functions] [replacement] [physics] [packages] [xact]
 

asked by codebpr https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=78049 Score of 2

10.9.3.2 Different answers from `NSurfaceIntegrate` if using `ImplicitRegion`

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=300596

I want to find the surface area of a region defined as $x^2+y^2\le1$ and $z=ln(x^2+y^2+2)$. 
I can transform it into cylindrical coordinates and write $z=ln(r^2+2)$. Using ... 
[numerical-integration]
 

asked by Deadbeef https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=98074 Score of 2

10.9.3.3 Regarding the interactive operation of a four-bar linkage mechanism

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=300700

I have a four-bar linkage mechanism, where when the left locator is moved, the right locator moves accordingly, and when the right locator is moved, the left locator moves accordingly. I have ... 
[manipulate] [dynamic] [animation] [simulation]
 

asked by miss https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=86487 Score of 2

answered by miss https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=86487 Score of 0