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Compute sums containing Clebsch Gordan coefficients?

Posted 3 months ago
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I'm trying to compute various sums which contain some CB coefficients, where the sum runs over the indexes m1,m2,m corresponding to each of the three angular momenta j1,j2,j. The thing is that when I try to evaluate such a sum, Mathematica shows some errors and then it throws the message "General::stop: Further output of ClebschGordan::phy will be suppressed during this calculation."

sum[j1_, j2_, j_] := 
  Sum[ClebschGordan[{j1, m1}, {j2, m2}, {j, m}], {m1, -j1, j1, 
    1}, {m2, -j2, j2, 1}, {m, -j, j, 1}];
N[sum[6, 2, 4]]
Do[Print[ClebschGordan[{6, m1}, {2, m2}, {4, m}]], {m1, -6, 6, 
  1}, {m2, -2, 2, 1}, {m, -4, 4, 1}]

I understand that for some values of {j1,m2},{j2,m2},{j,m} the CB coefficients are zero, but why does Mathematica throw error messages instead of just ignoring the term and keep going forward with the evaluation? Does the output error message mean that after a certain coefficient, Mathematica just simply stops evaluating terms, and my result will be incorrect?


I think you can just use Quiet to get rid of the error messages and you should be fine. You can even use Quiet @ Check[..., 0] to ensure that any terms that generate messages will be set to zero and don't affect the sum, if you're certain that that's the behavior you want.

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