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| bio | website | |
|---|---|---|
| location | ||
| age | ||
| visits | member for | 5 months |
| seen | 5 hours ago | |
| stats | profile views | 67 |
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2d |
accepted | Two questions about drawing tool |
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2d |
accepted | why set values in this way doesn't work? |
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May 7 |
accepted | why there is a small imaginary part |
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May 7 |
comment |
why there is a small imaginary part @bills thank you bill s. OK, I understand. |
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May 7 |
comment |
why there is a small imaginary part @bills it's not the problem of calculating eigenvalues. |
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May 7 |
asked | why there is a small imaginary part |
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May 6 |
comment |
direct assignment to the element in a Table But why boost2 doesn't have to be set to HoldAll?Of course, the code is more complicated than holdtable. It is a upsetdelayed and there is pattern match. But I didn't find the key to explain why the red in the definition of boost2 is valid. I found that if I don't let func to be Set when using boost2, for example, I write Join[boost2[test[1],tmp],{111,222}] then the tmp passed to Block has been evaluated. This confused me a lot. I seems boost2 is not perfect, right? |
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May 6 |
comment |
direct assignment to the element in a Table Thank you Mr.Wizard! I maybe a little anoying. But I have to make things clear, otherwise I will be very uncomfortable. Now I see I have to set HoldAll attribute to tobeheld, because otherwise it will be evaluated before being passed to Block. And I think that's why MMA make tobeheld red, the red is quite reasonable to prevent error. |
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May 5 |
revised |
A matrix-vector cross product added 274 characters in body |
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May 5 |
comment |
A matrix-vector cross product Ok, rule replacement works. But I still don't know where does it gone wrong? I looked into the Trace result, but it is unexpectedly long! I can't figure out why. |
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May 5 |
comment |
Confused about Unevaluated I think I understand. Clear explanation, Thank you very much! |
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May 5 |
comment |
A matrix-vector cross product OhOh, Sorry J.M. I found peculier things. Your solution is flawed. Try Cross[Unevaluated/@PauliMatrix[Range[3]],{0,1,0}] |
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May 5 |
comment |
Confused about Unevaluated What does inert mean? Are there any other head that are inert too? |
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May 5 |
comment |
Confused about Unevaluated Well, you mean the result of evaluating the head Unevaluated is just strip it, right? |
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May 5 |
comment |
A matrix-vector cross product I finally choose your answer. easier and won't have to worry about the order and negtive sign when using LeviCivitaTensor |
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May 5 |
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Confused about Unevaluated yeah! I notice it from Trace. Mathematica just simply strip Unevaluated away in the Table in the first step. But why? |
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May 5 |
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Confused about Unevaluated @m_goldberg thank you for recommending the very good book. |
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May 5 |
comment |
Confused about Unevaluated @MarkMcClure thank you very much |
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May 5 |
comment |
Confused about Unevaluated @MarkMcClure You're telling me that the step "then evaluate it" in Map and the step 'substitutes values ....explicitly evaluates the first argument at those values' in Table is two kind of evaluate?!! I still don't understand, Now that Table has the attributes HoldAll, it should hold the Unevaluated. It seems that "expr, shift+Enter" and "Evaluate[expr]" is different ? And Map use the first one Table use the second? |
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May 5 |
comment |
Confused about Unevaluated @MarkMcClure But according to the docs of Map. Map always effectively constructs a complete new expression and then evaluates it. And use Trace, I found in the last three steps, mathematica actually remove the Unevaluated, and finally bring back the Unevaluated head, why? |
