# What's in your differential geometry toolbox?

#### Aether

Gold Member
I saw GRTensorII mentioned here awhile back. What are the most powerful tools out there (which still run on a PC), including user manuals and texts, that you would recommend for working with field equations, curvature tensors, line elements, etc?

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#### Aether

Gold Member
I bought a copy of Maple 10, and am now trying to install GRTensorII. If there is anyone here who has already done this, could you please tell me exactly how you installed the library and .ini files?

#### pervect

Staff Emeritus
I have an old moldy version of maple, and not Maple 10. I never got the ini files to run automatically, I always had to run them manually, or paste them into a document when I ran GRTensor.

I also added a line to redefine the Christoffel symbols to my ini file:

grdef(CC{ ^a b c} := Chr{b c ^a});

By calculating CC(up,dn,dn), I get the Christoffel symbols in the format most textbooks use, rather than the peculiar format GRTensorII uses.

#### Aether

Gold Member
Thanks pervect.

I found a way to get the ini file to run automatically. Maple only executes the first .ini file that it finds in a subdirectory, so if you place a maple.ini file in the bin.win (or bin.wnt) subdirectory as instructed it won't execute because there is already a launch.ini file in that subdirectory.

The solution is to place the maple.ini file in the LIB subdirectory, and then it will execute on Maple startup.

My GRTensorII is now up and running with your suggested addition. However, it isn't loading libraries (such as basislib.m) automatically as it should.

#### smallphi

Aether, I am exactly at that point where I figured I had to put the maple.ini file in the LIB directory so it works but Maple complains it can't find basislib.m although it's there.

Have you found a solution for basislib.m?

#### George Jones

Staff Emeritus
Gold Member
Last edited by a moderator:

#### smallphi

I put maple.ini in the Users directory of Maple.

basislib.m is probably the library of commands working with bases and still doesn't want to load. Everything else works as before.

#### smallphi

I've figured it out. The GRTensorII webpage says

With Maple 8 and 9, for the current release of GRTensorII, you need to load the libraries needed for your calculation. In previous versions of Maple they autoload. A typical initialization file is here. Simply download this file and follow the instructions in it. If you have developed your own libraries, load them in the same way.
You have to use the maple.ini file they are talking about because it contains commands to load all the libraries at startup. The ini file that comes with the GRTensor package loads only the library with the main commands grii.m.

Alternatively, you can use the old maple.ini file but load the libraries you need manually. The Maple command to load basislib.m is

or you can use the GRTensor command

grlib(basislib);

After that everything works normal.

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#### smallphi

Has anyone found a way in GRTensor to display functions without the arguments to cleanup the output. I have a long expression and I want the function X(r,t) to display as X. The aliases in GRTensor work only for derivatives but not for the functions.

#### Aether

Gold Member
Check the path names in the maple.ini file to make sure that they are appropriate for where Grtii(6) is located on your hard drive, and put the maple.ini file in the Maple Users directory. Then start Maple and execute the commands "restart:" and then "grtw():" to get started.

If there are some commands that you are entering manually every time, like "grtw():", you can add those commands to the end of the maple.ini file and they will automatically execute when you start Maple, or execute the "restart:" command.

There are some sample worksheets in the "worksheets" folder of Grtii(6) where you can get some ideas about how to use the functions.

#### smallphi

Got this one too: use autoAlias if you want X(r,t) to be displayed as X.

The diffAlias creates aliases only for the partial derivatives not the function itself.

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#### smallphi

I don't like how the autoAlias works in GRtensor. It substitutes X with X(r,t) everywhere so later if you need to calculate something like the partical derivative diff(X(r,t), r), you have to write that as diff(X, r).

A better implementation of aliasing is given by the declare command in the PDEtools package. Just write

with(PDEtools); declare(X(r,t));

and all derivatives of X(r,t) including the function itself will be displayed without the arguments at the same time diff(X(r,t), r) will work normal. I don't know how declare() is implemented but it seems it substitutes X(r,t) with X only in the output, without creating alias for X(r,t) -> X.

#### Maestoso

Ok, sorry to raise a really old thread, but this has been annoying me all evening...

I've got GRTensor 1.79 working with Maple 10 quite happily; sorted out the ini files and loading of libraries and so on. My issue is when I type in "makeg(metricname);" it pastes some stuff to the screen but doesn't scroll it, and then pops up a message box and I don't know what I'm trying to enter. I much preferred the entry scheme in Maple 7 (what my old school had) where it prompted you to input the entry in the main window. Does anybody know how to get that form of entry working in Maple 10?

Thanks,
Jolyon

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