Tensor Network Theory Library
Beta release 1.1.1
A library of routines for performing TNTbased operations

The system has several global parameters that are used in all calculations. These can be based on the physical properties of your system, e.g. setting the basis operator and the global physical symmetries. In addition some of these are related to values used during calculations, for examples tolerances used in the SVD.
Functions  
void  tntFinalize (void) 
void  tntInitialize (void) 
void  tntMaxEigIterSet (int maxnum) 
void  tntReshapeReuseDisable (void) 
double  tntSVDRelTruncTolGet (void) 
void  tntSVDRelTruncTolSet (double relTruncTol) 
void  tntSVDRoutineSet (int svdtype) 
double  tntSVDTolGet (void) 
void  tntSVDTolSet (double inpTOL) 
double  tntSVDTruncTolGet (void) 
void  tntSVDTruncTolSet (double truncTol) 
unsigned  tntSymmNumGet (void) 
int  tntSymmTypeGet (void) 
void  tntSymmTypeSet (const char *symmTypeStr, unsigned num_qn) 
void  tntSymmTypeUnset (void) 
void  tntSysBasisOpFree (void) 
tntNode  tntSysBasisOpGet (void) 
void  tntSysBasisOpSet (tntNode basisOp) 
int  tntSysTypeGet (void) 
void  tntSysTypeSet (int sysnum) 
void  tntTruncType (const char *funcname) 
Variables  
tntSystem  systype 
void tntFinalize  (  void  ) 
Finalize the TNT library. Should follow all other TNT calls.
void tntInitialize  (  void  ) 
Initalize the TNT library and the system variables. Should precede all other TNT calls.
void tntMaxEigIterSet  (  int  maxnum  ) 
void tntReshapeReuseDisable  (  void  ) 
Disables the storage of the translations done in the reshape component. This will conserve memory but typically at a great expense computationally. It is recommended to use this function when the size of the tensors is constantly changing, for example in cases where the tolerance is set for the minimum size singular value to keep using tntSVDTruncTolSet().
double tntSVDRelTruncTolGet  (  void  ) 
Use this function to get the relative minimum for the singular values that will be kept in the SVD. Any singluar values which are `truncTol' times smaller than the maximum singluar value are be discarded, along with their associated right and left singular vectors. A negative value means that all singular values up to the value \(\chi\) are kept.
void tntSVDRelTruncTolSet  (  double  relTruncTol  ) 
Use this function to set a relative minimum for the singular values that will be kept in the SVD. Any singluar values which are `truncTol' times smaller than the maximum singluar value will be discarded, along with their associated right and left singluar vectors. Set to a negative value to ensure that all singular values up to the value \(\chi\) are kept (unless an absolute value has also been set).
Calling this function sets the tolerance for all subsequent SVDs. It is set to a negative value by default i.e. all singular values kept.
relTruncTol  The chosen tolerance. 
void tntSVDRoutineSet  (  int  svdtype  ) 
Use this function to change the SVD routine used in the core library. By default the LAPACK divide and conquer SVD is used (TNT_LAPACK_SDD). If you are having issues with the SVD converging or accuracy, please try using the LAPACK standard SVD (TNT_LAPACK_SVD). This performs more slowly but we have found it to be better behaved.
svdtype  The chose SVD type. Allowed values are TNT_LAPACK_SDD and TNT_LAPACK_SVD. 
double tntSVDTolGet  (  void  ) 
Get the tolerance below which values are treated as zero in the SVD.
void tntSVDTolSet  (  double  inpTOL  ) 
Sets the tolerance below which values are treated as zero in the SVD
inpTOL  The chosen tolerance. 
double tntSVDTruncTolGet  (  void  ) 
Use this function to get the absolute minimum for the singular values that will be kept in the SVD. Any singluar values which are smaller than `truncTol' will be discarded, along with their associated right and left singluar vectors. A negative value means that all singular values up to the value \(\chi\) are kept.
void tntSVDTruncTolSet  (  double  truncTol  ) 
Use this function to set an absolute minimum for the singular values that will be kept in the SVD. Any singluar values which are smaller than `truncTol' will be discarded, along with their associated right and left singluar vectors. Set to a negative value to ensure that all singular values up to the value \(\chi\) are kept (unless a relative value has also been set).
Calling this function sets the tolerance for all subsequent SVDs. It is set to a negative value by default i.e. all singular values kept. However, if there are any parts of your algorithm that take the inverse of nodes that result from an SVD, it is recommended to set this value (e.g. to 1e8) to ensure that your matrices are not singular.
truncTol  The chosen tolerance. 
unsigned tntSymmNumGet  (  void  ) 
Gets the number of seperate conserved quantities, or the number of quantum numbers required for a quantum number labels e.g for an twospecies system will return 2. The return value will be zero if no symmetry type is set.
int tntSymmTypeGet  (  void  ) 
Gets the symmetry type for the system, returning the result as an integer code more than 1, which will be one of the allowed symmetry types given by the defined variables. The return value will be TNT_SYMM_NONE if no symmetry type is set.
In the current version, the only currently allowed value is TNT_SYMM_U1.
void tntSymmTypeSet  (  const char *  symmTypeStr, 
unsigned  num_qn  
) 
Sets the symmetry type for the system. If it is set, then quantum number information is tracked, and the releavant quantities are conserved.
For example if U(1) is set (tntSymmetrySet("U(1)")
), and spin or boson operators created using tntMpsCreateSpinOp and tntMpsCreateBosonOp, and wave functions created using tntMpsCreateRandom() or tntMpsCreateConfig(), they will be set up to ensure that the total zprojection of spin or boson number are conserved respectively. This can significantly speed up calculations.
The argument num_qn
sets the number of seperate conserved quantities e.g. set to 2 for a two species system where the number of species 1 and the number of species 2 is conserved.
symmTypeStr  String denoting the symmetry type e.g. "U(1)" . 
num_qn  Number of separate conserved quantities. 
void tntSymmTypeUnset  (  void  ) 
Turns off keeping track of symmetries in the system. The quantum number information is removed from the basis operator, and library functions will no longer enforce number conservation.
Note that nodes that are in the blocked or symmetric format will be converted to VALS structure as they are encountered by library functions, rather than as soon as this function is called.
Note also that the SVD tolerance for zeroing values is turned back on to the default value of TNT_DEFAULT_TOL.
If symmetry information is not turned on prior to calling this function, it will have to effect.
void tntSysBasisOpFree  (  void  ) 
tntNode tntSysBasisOpGet  (  void  ) 
Returns the operator which defines the physical basis for the system. Note that this returns the handle to the actual basis operator, rather than a copy of it, so any modifications to it will alter the basis operator for the entire system. Therefore we recommend only inspecting properties of the operator rather than making changes to it unless you know exactly what you are doing.
void tntSysBasisOpSet  (  tntNode  basisOp  ) 
Sets the operator which defines the physical basis for the system. Note that a copy of the supplied node basisOp
is taken, so any changes can be made to basisOp
after the function has been called will not affect the system basis operator. Instead use tntSysBasisOpGet() to get a handle to the basis operator after this function has been called.
basisOp  Node that defines the basis operator 
int tntSysTypeGet  (  void  ) 
Returns a number which defines the type of system, where definitions for these numbers are given in the header file for the tier 2 library being used. Currently the only tier 2 library is libtntMps, which can give the values TNT_MPS_SPIN and TNT_MPS_BOSON.
void tntSysTypeSet  (  int  sysnum  ) 
Sets the system type using the integer code given. Note that no checks are made that the integer given actually corresponds to a system type known by the tier 2 library  users can define custom system types if they wish.
See the header or documentation for your tier 2 library for the currently supported system types. Currently the only tier 2 library is libtntMps, which can give the values TNT_MPS_SPIN and TNT_MPS_BOSON.
sysnum  Number code defining the system type. 
void tntTruncType  (  const char *  funcname  ) 
Sets the function used to calculate the truncation error \(e_{\mathrm{trunc}}\) when taking the SVD of a node. Once this function is set the same truncation type will be used for all subsequent calculations, unless it is called again a different argument. Note the choice will automatically be saved to any output file, and reloaded when that file is loaded. The currently supported truncation types are:
'sumsquares'
The error is given by the sum of the squares of the discarded singluar values i.e.
\[ e_{\mathrm{trunc}} = \sum_{j=\chi}^{\chi_{\mathrm{orig}}1} S_{j}^2. \]
'1norm'
The error is given by the 1norm of the discarded singluar values i.e.
\[ e_{\mathrm{trunc}} = \sum_{j=\chi}^{\chi_{\mathrm{orig}}1} S_{j}. \]
'1normscaled'
The error is given by the 1norm of the discarded singluar values divided by the 1norm of all the singular values i.e.
\[ e_{\mathrm{trunc}} = \left( \sum_{j=\chi}^{\chi_{\mathrm{orig}}1} S_{j} \right)\Bigg{/}\left( \sum_{j=0}^{\chi_{\mathrm{orig}}1} S_{j} \right). \]
'2norm'
The the error \(e\) is given by the 2norm of the discarded singluar values i.e.
\[ e_{\mathrm{trunc}} = \left( \sum_{j=\chi}^{\chi_{\mathrm{orig}}1} S_{j}^2 \right)^{1/2}. \]
'2normscaled'
The error \(e\) is given by the 2norm of the discarded singluar values divided by the 2norm of all the singular values i.e.
\[ e_{\mathrm{trunc}} = \left( \sum_{j=\chi}^{\chi_{\mathrm{orig}}1} S_{j}^2 \right)^{1/2}\Bigg{/}\left( \sum_{j=0}^{\chi_{\mathrm{orig}}1} S_{j}^2 \right)^{1/2}. \]
In all the above cases, the indexing in the sum starts from zero. The default is '2norm', and will be used if no value is set using this function.
funcname  The name of desired truncation type e.g. "sumsquares". 