void UniformHelmholtzGreens
( ElementalMatrix<Complex<Real>>& A, Int n, Real lambda )
{
EL_DEBUG_CSE
typedef Complex<Real> C;
const Real pi = 4*Atan( Real(1) );
const Real k0 = 2*pi/lambda;
const Grid& g = A.Grid();
// Generate a list of n uniform samples from the 3D unit ball
DistMatrix<Real,STAR,VR> X_STAR_VR(3,n,g);
for( Int jLoc=0; jLoc<X_STAR_VR.LocalWidth(); ++jLoc )
{
Real x0, x1, x2;
// Sample uniformly from [-1,+1]^3 until a point is drawn from the ball
while( true )
{
x0 = SampleUniform( Real(-1), Real(1) );
x1 = SampleUniform( Real(-1), Real(1) );
x2 = SampleUniform( Real(-1), Real(1) );
const Real radiusSq = x0*x0 + x1*x1 + x2*x2;
if( radiusSq > 0 && radiusSq <= 1 )
break;
}
X_STAR_VR.SetLocal( 0, jLoc, x0 );
X_STAR_VR.SetLocal( 1, jLoc, x1 );
X_STAR_VR.SetLocal( 2, jLoc, x2 );
}
DistMatrix<Real,STAR,STAR> X_STAR_STAR( X_STAR_VR );
A.Resize( n, n );
for( Int jLoc=0; jLoc<A.LocalWidth(); ++jLoc )
{
const Int j = A.GlobalCol(jLoc);
const Real xj0 = X_STAR_STAR.GetLocal(0,j);
const Real xj1 = X_STAR_STAR.GetLocal(1,j);
const Real xj2 = X_STAR_STAR.GetLocal(2,j);
for( Int iLoc=0; iLoc<A.LocalHeight(); ++iLoc )
{
const Int i = A.GlobalRow(iLoc);
if( i == j )
{
A.SetLocal( iLoc, jLoc, 0 );
}
else
{
const Real d0 = X_STAR_STAR.GetLocal(0,i)-xj0;
const Real d1 = X_STAR_STAR.GetLocal(1,i)-xj1;
const Real d2 = X_STAR_STAR.GetLocal(2,i)-xj2;
const Real gamma = k0*Sqrt(d0*d0+d1*d1+d2*d2);
const Real realPart = Cos(gamma)/gamma;
const Real imagPart = Sin(gamma)/gamma;
A.SetLocal( iLoc, jLoc, C(realPart,imagPart) );
}
}
}
}
void MakeExtendedKahan
( ElementalMatrix<F>& A, Base<F> phi, Base<F> mu )
{
EL_DEBUG_CSE
typedef Base<F> Real;
if( A.Height() != A.Width() )
LogicError("Extended Kahan matrices must be square");
const Int n = A.Height();
if( n % 3 != 0 )
LogicError("Dimension must be an integer multiple of 3");
const Int l = n / 3;
if( !l || (l & (l-1)) )
LogicError("n/3 is not a power of two");
Int k=0;
while( Int(1u<<k) < l )
++k;
if( phi <= Real(0) || phi >= Real(1) )
LogicError("phi must be in (0,1)");
if( mu <= Real(0) || mu >= Real(1) )
LogicError("mu must be in (0,1)");
// Start by setting A to the identity, and then modify the necessary
// l x l blocks of its 3 x 3 partitioning.
MakeIdentity( A );
unique_ptr<ElementalMatrix<F>> ABlock( A.Construct(A.Grid(),A.Root()) );
View( *ABlock, A, IR(2*l,3*l), IR(2*l,3*l) );
*ABlock *= mu;
View( *ABlock, A, IR(0,l), IR(l,2*l) );
Walsh( *ABlock, k );
*ABlock *= -phi;
View( *ABlock, A, IR(l,2*l), IR(2*l,3*l) );
Walsh( *ABlock, k );
*ABlock *= phi;
// Now scale A by S
const Real zeta = Sqrt(Real(1)-phi*phi);
auto& ALoc = A.Matrix();
for( Int iLoc=0; iLoc<A.LocalHeight(); ++iLoc )
{
const Int i = A.GlobalRow(iLoc);
const Real gamma = Pow(zeta,Real(i));
for( Int jLoc=0; jLoc<A.LocalWidth(); ++jLoc )
ALoc(iLoc,jLoc) *= gamma;
}
}
void IndexDependentMap
( const ElementalMatrix<S>& A,
ElementalMatrix<T>& B,
function<T(Int,Int,S)> func )
{
DEBUG_CSE
const Int mLoc = A.LocalHeight();
const Int nLoc = A.LocalWidth();
B.AlignWith( A.DistData() );
B.Resize( A.Height(), A.Width() );
auto& ALoc = A.LockedMatrix();
auto& BLoc = B.Matrix();
for( Int jLoc=0; jLoc<nLoc; ++jLoc )
{
const Int j = A.GlobalCol(jLoc);
for( Int iLoc=0; iLoc<mLoc; ++iLoc )
{
const Int i = A.GlobalRow(iLoc);
BLoc(iLoc,jLoc) = func(i,j,ALoc(iLoc,jLoc));
}
}
}