QDP++ Quick Reference

1 Description

QDP++ is a C++ data-parallel interface for Lattice field theory applications. Many of the issues have been discussed in the corresponding C interface description which can be found at http://www.jlab.org/~edwards/qcdapi/Level2API_latest.pdf. The motivation for this development comes from the U.S. Dept. of Energy SciDAC program.

The QDP interface provides an environment somewhat similar to Fortran 90 - namely data-parallel operations (operator/infix form) which can be applied on lattice wide objects. The interface provides a level of abstraction such that high-level user code written using the API can be run unchanged on a single processor workstation or a collection of multiprocessor nodes with parallel communications. Architectural dependencies are hidden below the interface. A variety of types for the site elements are provided. To achieve good performance, overlapping communication and computation primitives are provided.

2 Supported operations

All QDP objects are of type

QDPType. Supported operations are listed below. Con-
vention: protoyypes are basically of the form:

QDPType    unary_function(const QDPType&)
QDPType    binary_function(const QDPType&, const QDPType&)

2.1 Subsets

Set::Make(int func(),int num) : Set construction of ordinality num subsets.
                                func maps coordinates to a coloring in [0,num)

2.2 Infix operators

Unary infix (e.g., ”operator-”):

- : negation
+ : unaryplus
~ : bitwise not
! : boolean not

Binary infix (e.g., ”operator+”):

+ : addition
- : subtraction
* : multiplication
/ : division
% : mod
& : bitwise and
| : bitwise or
^ : bitwise exclusive or
<< : left-shift
>> : right-shift

Comparisons (returning booleans, e.g., ”operator<”):

<, <=, >, >=, ==, !=
&& : and of 2 booleans
|| : or of 2 boolean

Assignments (e.g., ”operator+=”):

=, +=, -=, *=, /=, %=, |=, &=, ^=, <<=, >>=

Trinary:

where(bool,arg1,arg2) : the C trinary "?" operator -> (bool) ? arg1 : arg2

2.3 Functions (standard C math lib)

Unary:

cos, sin, tan, acos, asin, atan, cosh, sinh, tanh,
exp, log, log10, sqrt,
ceil, floor, fabs

Binary:

ldexp, pow, fmod, atan2

2.4 Additional functions (specific to QDP)

Unary:

conj                 : hermitian conjugate (adjoint)
trace                : matrix trace
real                 : real part
imag                 : imaginary part
colorTrace           : trace over color indices
spinTrace            : trace over spin indices
multiplyI            : multiplies argument by imag "i"
multiplyMinusI       : multiplies argument by imag "-i"
localNorm2           : on fibers computes trace(conj(source)*source)

Binary:

cmplx                 : returns complex object   arg1 + i*arg2
localInnerproduct     : at each site computes trace(conj(arg1)*arg2)

2.5 In place functions

random(dest)            : uniform random numbers - all components
gaussian(dest)          : uniform random numbers - all components
zero(dest)              : zero out all elements
copymask(dest,mask,src) : copy src to dest under boolean mask

2.6 Global reductions

sum(arg1)               : sum over lattice indices returning
                          object of same fiber type
norm2(arg1)             : sum(localNorm2(arg1))
innerproduct(arg1,arg2) : sum(localInnerproduct(arg1,arg2))
sumMulti(arg1,Set)      : sum over each subset of Set returning #subset
                          objects of same fiber type

2.7 Accessors

Peeking and poking (accessors) into various component indices of objects.

peekSite(arg1,multi1d<int> coords): return site object of primitive type of arg1
peekColor(arg1,int row,int col)   : return object from color matrix elem row and col
peekColor(arg1,int row)           : return object from color vector elem row
peekSpin(arg1,int row,int col )   : return object from spin matrix elem row and col
peekSpin(arg1,int row)            : return object from spin vector elem row

pokeSite(dest,src,multi1d<int> coords): insert src at site given by coords
pokeColor(dest,src,int row,int col)   : insert src into color matrix elem row and col
pokeColor(dest,src,int row)           : insert src into color vector elem row
pokeSpin(dest,src,int row,int col )   : insert src into spin matrix elem row and col
pokeSpin(dest,src,int row)            : insert src into spin vector elem row

2.8 More exotic functions:

Gauge and spin related functions.

`spinProject(QDPType psi, int dir, int isign)`

Applies spin projection of $(1 + \mathrm{isign} \gamma_\mu)\,\mathrm{psi}$ , returning a half spin vector or matrix.

`spinReconstruct(QDPType psi, int dir, int isign)`

Applies spin reconstruction of $(1 + \mathrm{isign} \gamma_\mu)\,\mathrm{psi}$ , returning a full spin vector or matrix.