This summation sums to zero. Why?

  • Thread starter EngWiPy
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  • #1
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Hi,

I am reading a paper, and at some point the authors claim that:

[tex]\sum_{m=1}^{L+1}\frac{\prod_{\substack{l=1\\l\neq m}}^{L+1}\frac{\lambda(m)}{\lambda(m)-\lambda(l)}}{\lambda^r(m)}=0[/tex]

the question is HOW?

Any tiny hint will be highly appreciated.

Thanks
 

Answers and Replies

  • #2
38
0
In general there is no equality.
It must depend on the definitions of λ, r and L.
Can you provide more details?
 
  • #3
1,367
61
In general there is no equality.
It must depend on the definitions of λ, r and L.
Can you provide more details?

Lambdas are positive numbers, r is between 1 and L. That is all
 
  • #4
38
0
I don't think that is correct.

Define [itex]\lambda(m)=m[/itex], and pick [itex]L=r=2[/itex]. Then
[tex]\frac{\frac{\lambda(1)}{\left(\lambda(1)-\lambda(2)\right)\left(\lambda(1)-\lambda(3)\right)}}{\lambda(1)^2}+\frac{\frac{\lambda(2)}{\left(\lambda(2)-\lambda(1)\right)\left(\lambda(2)-\lambda(3)\right)}}{\lambda(2)^2}+\frac{\frac{\lambda(3)}{\left(\lambda(3)-\lambda(1)\right)\left(\lambda(3)-\lambda(2)\right)}}{\lambda(3)^2}=\frac{1}{2}-\frac{1}{2}+\frac{1}{6}=\frac{1}{6}[/tex]
 

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