Square root ising

[JoeyT1994]

Added Functions to specialitensornetworks.jl for creating the Tensor Network State corresponding to the square root of the classical ising partition function.

Also:

i) Removed a repeated docstring.
ii) Specified the link_space argument in ising_network so it works for both an index network with siteinds and without.

[mtfishman]

Thanks, nice to see that you can mostly make use of the existing ising_network function.

[mtfishman]

@JoeyT1994 looks like this broke a BP test.

[codecov-commenter]

Codecov Report

Merging #76 (f9916d5) into main (741a28f) will decrease coverage by 0.20%.
The diff coverage is 0.00%.

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@@            Coverage Diff             @@
##             main      #76      +/-   ##
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- Coverage   77.79%   77.59%   -0.20%     
==========================================
  Files          61       61              
  Lines        3233     3241       +8     
==========================================
  Hits         2515     2515              
- Misses        718      726       +8     

Impacted Files	Coverage Δ
src/specialitensornetworks.jl	71.87% <0.00%> (-10.27%)	⬇️

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[JoeyT1994]

Okay I see. I fixed it now with the latest commit.

[mtfishman]

Maybe ising_network_state would be a better name? square_root doesn't seem quite right for this (it's more that it is a state such that the norm of the state gives the Ising model).

[mtfishman]

Thanks Joey, this will be very nice to have!