Residue Calculus Integrable Model

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I'm currently working on the derivation of Bethe ansatz equations.



I have an equation like this:



$ z^-1prod_m=1,mneq l^Q-1fracq^2z-z_mz-z_m+q^-2z
prod_m=1,mneq l^Q-1fracq^-2z-z_mz-z_m-(z+z^-1)=E,$



where $zin mathbbC,qinmathbbC$ and $E$ is an energy eigenvalue.



Obviously, the poles exist at $z=0, z=infty , z=z_m$. Since the lhs is meromorphic function and the rhs is a constant, to make them equal, I have to calculate the residues and null them.



For $z=0$ the problem is solved. But I have problem with the two other cases.



I tried to calculate the residue at $z=infty$ and at $z=z_m$ via



$Res(f(z),z=infty)=-Res(-z^-2f(1/z),z=0)$ and $ Res(f(z),z=z_m)=lim_zto z_m(z-z_m)cdots$



The vanishing of the resiude at $z=z_m$ should give equations like this:



$z^2_l=q^Qprod_m=1,mneq l^Q-1 fracq^2 z_l -z_mz_l-q^2z_m$



But in both cases I failed. Please, can anybody help. I am grateful for any ideas.







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  • ‘Calculate the residue and then null them’ what do you mean, practically?
    – Szeto
    Aug 1 at 0:55










  • I mean that the residues , e.g. at $z=z_m$ vanish if the parameters $lbrace z_l rbrace$ satisfy the above equation $z^2_l=cdots$. Does this help you?
    – Herrmann Dirac-Neumann
    Aug 1 at 9:49















up vote
0
down vote

favorite












I'm currently working on the derivation of Bethe ansatz equations.



I have an equation like this:



$ z^-1prod_m=1,mneq l^Q-1fracq^2z-z_mz-z_m+q^-2z
prod_m=1,mneq l^Q-1fracq^-2z-z_mz-z_m-(z+z^-1)=E,$



where $zin mathbbC,qinmathbbC$ and $E$ is an energy eigenvalue.



Obviously, the poles exist at $z=0, z=infty , z=z_m$. Since the lhs is meromorphic function and the rhs is a constant, to make them equal, I have to calculate the residues and null them.



For $z=0$ the problem is solved. But I have problem with the two other cases.



I tried to calculate the residue at $z=infty$ and at $z=z_m$ via



$Res(f(z),z=infty)=-Res(-z^-2f(1/z),z=0)$ and $ Res(f(z),z=z_m)=lim_zto z_m(z-z_m)cdots$



The vanishing of the resiude at $z=z_m$ should give equations like this:



$z^2_l=q^Qprod_m=1,mneq l^Q-1 fracq^2 z_l -z_mz_l-q^2z_m$



But in both cases I failed. Please, can anybody help. I am grateful for any ideas.







share|cite|improve this question



















  • ‘Calculate the residue and then null them’ what do you mean, practically?
    – Szeto
    Aug 1 at 0:55










  • I mean that the residues , e.g. at $z=z_m$ vanish if the parameters $lbrace z_l rbrace$ satisfy the above equation $z^2_l=cdots$. Does this help you?
    – Herrmann Dirac-Neumann
    Aug 1 at 9:49













up vote
0
down vote

favorite









up vote
0
down vote

favorite











I'm currently working on the derivation of Bethe ansatz equations.



I have an equation like this:



$ z^-1prod_m=1,mneq l^Q-1fracq^2z-z_mz-z_m+q^-2z
prod_m=1,mneq l^Q-1fracq^-2z-z_mz-z_m-(z+z^-1)=E,$



where $zin mathbbC,qinmathbbC$ and $E$ is an energy eigenvalue.



Obviously, the poles exist at $z=0, z=infty , z=z_m$. Since the lhs is meromorphic function and the rhs is a constant, to make them equal, I have to calculate the residues and null them.



For $z=0$ the problem is solved. But I have problem with the two other cases.



I tried to calculate the residue at $z=infty$ and at $z=z_m$ via



$Res(f(z),z=infty)=-Res(-z^-2f(1/z),z=0)$ and $ Res(f(z),z=z_m)=lim_zto z_m(z-z_m)cdots$



The vanishing of the resiude at $z=z_m$ should give equations like this:



$z^2_l=q^Qprod_m=1,mneq l^Q-1 fracq^2 z_l -z_mz_l-q^2z_m$



But in both cases I failed. Please, can anybody help. I am grateful for any ideas.







share|cite|improve this question











I'm currently working on the derivation of Bethe ansatz equations.



I have an equation like this:



$ z^-1prod_m=1,mneq l^Q-1fracq^2z-z_mz-z_m+q^-2z
prod_m=1,mneq l^Q-1fracq^-2z-z_mz-z_m-(z+z^-1)=E,$



where $zin mathbbC,qinmathbbC$ and $E$ is an energy eigenvalue.



Obviously, the poles exist at $z=0, z=infty , z=z_m$. Since the lhs is meromorphic function and the rhs is a constant, to make them equal, I have to calculate the residues and null them.



For $z=0$ the problem is solved. But I have problem with the two other cases.



I tried to calculate the residue at $z=infty$ and at $z=z_m$ via



$Res(f(z),z=infty)=-Res(-z^-2f(1/z),z=0)$ and $ Res(f(z),z=z_m)=lim_zto z_m(z-z_m)cdots$



The vanishing of the resiude at $z=z_m$ should give equations like this:



$z^2_l=q^Qprod_m=1,mneq l^Q-1 fracq^2 z_l -z_mz_l-q^2z_m$



But in both cases I failed. Please, can anybody help. I am grateful for any ideas.









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asked Jul 31 at 23:08









Herrmann Dirac-Neumann

1




1











  • ‘Calculate the residue and then null them’ what do you mean, practically?
    – Szeto
    Aug 1 at 0:55










  • I mean that the residues , e.g. at $z=z_m$ vanish if the parameters $lbrace z_l rbrace$ satisfy the above equation $z^2_l=cdots$. Does this help you?
    – Herrmann Dirac-Neumann
    Aug 1 at 9:49

















  • ‘Calculate the residue and then null them’ what do you mean, practically?
    – Szeto
    Aug 1 at 0:55










  • I mean that the residues , e.g. at $z=z_m$ vanish if the parameters $lbrace z_l rbrace$ satisfy the above equation $z^2_l=cdots$. Does this help you?
    – Herrmann Dirac-Neumann
    Aug 1 at 9:49
















‘Calculate the residue and then null them’ what do you mean, practically?
– Szeto
Aug 1 at 0:55




‘Calculate the residue and then null them’ what do you mean, practically?
– Szeto
Aug 1 at 0:55












I mean that the residues , e.g. at $z=z_m$ vanish if the parameters $lbrace z_l rbrace$ satisfy the above equation $z^2_l=cdots$. Does this help you?
– Herrmann Dirac-Neumann
Aug 1 at 9:49





I mean that the residues , e.g. at $z=z_m$ vanish if the parameters $lbrace z_l rbrace$ satisfy the above equation $z^2_l=cdots$. Does this help you?
– Herrmann Dirac-Neumann
Aug 1 at 9:49
















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