## Learn to Use ITensor

main / classes / iqindexval C++v3 | C++v2

# IQIndexVal

IQIndexVal conceptually represents an IQIndex fixed to a specific value.

An IQIndexVal holds both an IQIndex .index and an integer .val representing a particular value the IQIndex can take. The value is 1-indexed and must be in the range [1,m] where m is the size of the IQIndex.

IQIndexVals correspond to a specific block of their associated IQIndex. Consider an IQIndexVal iv associated with an IQIndex I having two blocks, both of size 8. If iv.val <= 8 it corresponds to the first block of I. If iv.val > 8 it corresponds to the second block of I.

IQIndexVal is defined in the header "itensor/iqindex.h".

## Synopsis

auto I = IQIndex("I",Index("I+1",8),QN(+1),
Index("I-1",8),QN(-1));

auto iv = IQIndexVal(I,9);

Print(iv.index == I); //prints: true
Print(iv.val == 9);   //prints: true

Print(iv.qn()); //prints: QN(-1)


## Public Data Members

• IQIndex index

• long val

## Class Methods

• IQIndexVal(IQIndex I, long val)

Constructor taking an IQIndex I and value val.
After constructing an IQIndexVal iv, the data members
iv.index == I and iv.val == val.

• .qn() -> QN

Return the quantum number of the block corresponding to this IQIndexVal.

• .indexqn() -> IndexQN

Return an IndexQN whose Index and QN are those of the block corresponding to this IQIndexVal.

• explicit operator IndexVal()

Explicit cast IQIndexVal to IndexVal. The resulting IndexVal has the property:

• .index is the result of casting the IQIndexVal's IQIndex to just an Index
• .val is unchanged

Conceptually this cast views the associated IQIndex as just an Index, ignoring its block structure.

• .blockIndexVal() -> IndexVal

Return an IndexVal with the following properties:

• .index is the block index corresponding to the block of the IQIndexVal
• .val is the relative offset within the block of the IQIndexVal

For example, if an IQIndexVal has value 11, then if the IQIndex is such that the first block has size 3; second block has size 6; and third block 3 has size 8; then the IQIndexVal falls inside (corresponds to) the third block, and has relative offset 2 (=11-6-3).

• .dag()

Reverse the Arrow direction of the .index field of this IQIndexVal.

• .prime(IndexType type, int inc = 1)

Increment the primelevel of .index if its IndexType matches type by 1, or by an optional amount inc.

• .noprime(IndexType type = All)

Set the primelevel of .index to zero (optionally only if its IndexType matches type).

• .mapprime(int plevold, int plevnew, IndexType type = All)

If the primelevel of .index is plevold, change it to plevnew (optionally only if its IndexType matches type).

## Other IQIndexVal Features

• IQIndexVals are default constructible.

• IQIndexVals compare equal if both their .index and .val members are equal.

• IQIndexVals can be compared to an IQIndex, in which case only the .index field is used.

## IQIndexVal Functions

• dag(IQIndexVal iv) -> IQIndexVal

Return a copy of the IQIndexVal with the Arrow direction of its .index reversed.

• prime(IQIndexVal iv, IndexType type, int inc = 1) -> IQIndexVal

Return a copy of the IQIndexVal iv, incrementing the primelevel of its .index field if its IndexType matches type by 1, or by an optional amount inc.

• noprime(IQIndexVal iv, IndexType type = All) -> IQIndexVal

Return a copy of the IQIndexVal iv, setting the primelevel of its .index field to zero (optionally only if its IndexType matches type).

• mapprime(IQIndexVal iv, int plevold, int plevnew, IndexType type = All) -> IQIndexVal

Return a copy of the IQIndexVal iv such that if the primelevel of its .index field is plevold, it is changed to plevnew (optionally only if its IndexType matches type).