# Tag Info

1

If you are using Mathematica version 9, the best approach is probably to use the new symbolic tensor functionality as suggested by zentient. However for this problem it may be sufficient to explicitly specify a rule to convert expressions like Norm[-q] into Norm[q]: myform = Expand[# /. Norm[-x_ + y_.] :> Norm[x - y]] &; (F2s[q, k1]*F2s[-q, k2]) // ...

12

It took me quite a while, but finally, here's a visualization of the perigee of Flamsteed's comet: I should first note two things: first, some of the needed data for computing the orbit of comet C/1683 O1 was missing in AstronomicalData["CometC1683O1", "Properties"], and I had to pull information from external sources to supplement the information ...

4

Based on the assumption that those F functions produce scalar results… If you just want to manipulate the vectors as entities without considering their components, then you can enter the function for F2s f2s[q_, k1_] := (5/ 14) + (3 (Norm[k1])^2)/(28 (Norm[q])^2) + (3 Norm[ k1]^2)/(28 (Norm[q - k1])^2) - (5)/(28 (Norm[q])^2 (Norm[ q - k1])^(-2)) - ...

5

The problem is that Mathematica prematurely threads r[t] - p not knowing r[t] is actually in $\mathbb{R}^2$ In[]:= r[t]-{0,0} Out[]= {r[t],r[t]} Which is not what you want. A quick fix for these types of issues is to create a function that only evaluates for numerical values (Changed to NDSolve since I only have v8): dummy[r_?(VectorQ[#, NumericQ] ...

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