The solution is fairly straightforward – since GRTensor is looking for the file metrics:schw.mpl, all we need to do is make sure our file is named as such and GRTensor will be able to find it (Note that the file must also reside in the directory GRTensor is installed in, not the metrics subdirectory). GRTensor appears to be trying to use the old, pre-OSX colon system, so it mistakenly searches for metrics:schw, which it obviously can’t find. Historically, Mac OS used the colon as a path separator but, since OSX, it uses the more unix-like slash. The problem seems to arise from the way GRTensor deals with path separators on the Mac. This error is telling us that GRTensor isn’t able to find the schw metric, even though we know it is present in the metrics directory. Error, (in qload) Could not find metric schw2 When you do so, you are presented with the following error: > qload(schw2) Warning: grOptionMetricPath has not been assigned. The bug is triggered whenever you try to load a metric, which is usually the first thing you would do in a GRTensor session. Fortunately, there is a straightforwarde solution. This is due to a bug in GRTensor that has gone unfixed for quite a while. Unfortunately, getting it working on Mac OS X is a bit of a pain. ![]() You can define your own tensors or use the predefined ones. ![]() Given a specific metric, it’s great at calculating the components of tensors. ![]() ![]() GRTensor is a very handy Maple package for doing calculations in General Relativity.
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