private void updateAlphaVec()
{
// Function calculates the alpha vector with given
// fixed pillars+values
// Write Matrix M
double tmp = 0.0;
for (int rowIt = 0; rowIt < xSize_; ++rowIt)
{
yVec_[rowIt] = this.yBegin_[rowIt];
tmp = 1.0 / gammaFunc(this.xBegin_[rowIt]);
for (int colIt = 0; colIt < xSize_; ++colIt)
{
M_[rowIt, colIt] = kernelAbs(this.xBegin_[rowIt],
this.xBegin_[colIt]) * tmp;
}
}
// Solve y=M*\alpha for \alpha
alphaVec_ = MatrixUtilities.qrSolve(M_, yVec_);
// check if inversion worked up to a reasonable precision.
// I've chosen not to check determinant(M_)!=0 before solving
Vector test = M_ * alphaVec_;
Vector diffVec = Vector.Abs((M_ * alphaVec_) - yVec_);
for (int i = 0; i < diffVec.size(); ++i)
{
Utils.QL_REQUIRE(diffVec[i] < invPrec_, () =>
"Inversion failed in 1d kernel interpolation");
}
}
private void updateAlphaVec()
{
// Function calculates the alpha vector with given
// fixed pillars+values
Vector Xk = new Vector(2), Xn = new Vector(2);
int rowCnt = 0, colCnt = 0;
double tmpVar = 0.0;
// write y-vector and M-Matrix
for (int j = 0; j < ySize_; ++j)
{
for (int i = 0; i < xSize_; ++i)
{
yVec_[rowCnt] = this.zData_[i, j];
// calculate X_k
Xk[0] = this.xBegin_[i];
Xk[1] = this.yBegin_[j];
tmpVar = 1 / gammaFunc(Xk);
colCnt = 0;
for (int jM = 0; jM < ySize_; ++jM)
{
for (int iM = 0; iM < xSize_; ++iM)
{
Xn[0] = this.xBegin_[iM];
Xn[1] = this.yBegin_[jM];
M_[rowCnt, colCnt] = kernelAbs(Xk, Xn) * tmpVar;
colCnt++; // increase column counter
}// end iM
}// end jM
rowCnt++; // increase row counter
} // end i
}// end j
alphaVec_ = MatrixUtilities.qrSolve(M_, yVec_);
// check if inversion worked up to a reasonable precision.
// I've chosen not to check determinant(M_)!=0 before solving
Vector diffVec = Vector.Abs(M_ * alphaVec_ - yVec_);
for (int i = 0; i < diffVec.size(); ++i)
{
Utils.QL_REQUIRE(diffVec[i] < invPrec_, () =>
"inversion failed in 2d kernel interpolation");
}
}
//! QR Solve
/*! This implementation is based on MINPACK
* (<http://www.netlib.org/minpack>,
* <http://www.netlib.org/cephes/linalg.tgz>)
*
* Given an m by n matrix A, an n by n diagonal matrix d,
* and an m-vector b, the problem is to determine an x which
* solves the system
*
* A*x = b , d*x = 0 ,
*
* in the least squares sense.
*
* d is an input array of length n which must contain the
* diagonal elements of the matrix d.
*
* See lmdiff.cpp for further details.
*/
public static Vector qrSolve(Matrix a, Vector b, bool pivot = true, Vector d = null)
{
int m = a.rows();
int n = a.columns();
if (d == null)
{
d = new Vector();
}
Utils.QL_REQUIRE(b.Count == m, () => "dimensions of A and b don't match");
Utils.QL_REQUIRE(d.Count == n || d.empty(), () => "dimensions of A and d don't match");
Matrix q = new Matrix(m, n), r = new Matrix(n, n);
List <int> lipvt = MatrixUtilities.qrDecomposition(a, ref q, ref r, pivot);
List <int> ipvt = new List <int>(n);
ipvt = lipvt;
//std::copy(lipvt.begin(), lipvt.end(), ipvt.get());
Matrix aT = Matrix.transpose(a);
Matrix rT = Matrix.transpose(r);
Vector sdiag = new Vector(n);
Vector wa = new Vector(n);
Vector ld = new Vector(n, 0.0);
if (!d.empty())
{
ld = d;
//std::copy(d.begin(), d.end(), ld.begin());
}
Vector x = new Vector(n);
Vector qtb = Matrix.transpose(q) * b;
MINPACK.qrsolv(n, rT, n, ipvt, ld, qtb, x, sdiag, wa);
return(x);
}
//! Returns the pseudo square root of a real symmetric matrix
/*! Given a matrix \f$ M \f$, the result \f$ S \f$ is defined
* as the matrix such that \f$ S S^T = M. \f$
* If the matrix is not positive semi definite, it can
* return an approximation of the pseudo square root
* using a (user selected) salvaging algorithm.
*
* For more information see: "The most general methodology to create
* a valid correlation matrix for risk management and option pricing
* purposes", by R. Rebonato and P. Jдckel.
* The Journal of Risk, 2(2), Winter 1999/2000
* http://www.rebonato.com/correlationmatrix.pdf
*
* Revised and extended in "Monte Carlo Methods in Finance",
* by Peter Jдckel, Chapter 6.
*
* \pre the given matrix must be symmetric.
*
* \relates Matrix
*
* \warning Higham algorithm only works for correlation matrices.
*
* \test
* - the correctness of the results is tested by reproducing
* known good data.
* - the correctness of the results is tested by checking
* returned values against numerical calculations.
*/
public static Matrix pseudoSqrt(Matrix matrix, SalvagingAlgorithm sa)
{
int size = matrix.rows();
#if QL_EXTRA_SAFETY_CHECKS
checkSymmetry(matrix);
#else
if (size != matrix.columns())
{
throw new Exception("non square matrix: " + size + " rows, " + matrix.columns() + " columns");
}
#endif
// spectral (a.k.a Principal Component) analysis
SymmetricSchurDecomposition jd = new SymmetricSchurDecomposition(matrix);
Matrix diagonal = new Matrix(size, size, 0.0);
// salvaging algorithm
Matrix result = new Matrix(size, size);
bool negative;
switch (sa)
{
case SalvagingAlgorithm.None:
// eigenvalues are sorted in decreasing order
if (!(jd.eigenvalues()[size - 1] >= -1e-16))
{
throw new Exception("negative eigenvalue(s) (" + jd.eigenvalues()[size - 1] + ")");
}
result = MatrixUtilities.CholeskyDecomposition(matrix, true);
break;
case SalvagingAlgorithm.Spectral:
// negative eigenvalues set to zero
for (int i = 0; i < size; i++)
{
diagonal[i, i] = Math.Sqrt(Math.Max(jd.eigenvalues()[i], 0.0));
}
result = jd.eigenvectors() * diagonal;
normalizePseudoRoot(matrix, result);
break;
case SalvagingAlgorithm.Hypersphere:
// negative eigenvalues set to zero
negative = false;
for (int i = 0; i < size; ++i)
{
diagonal[i, i] = Math.Sqrt(Math.Max(jd.eigenvalues()[i], 0.0));
if (jd.eigenvalues()[i] < 0.0)
{
negative = true;
}
}
result = jd.eigenvectors() * diagonal;
normalizePseudoRoot(matrix, result);
if (negative)
{
result = hypersphereOptimize(matrix, result, false);
}
break;
case SalvagingAlgorithm.LowerDiagonal:
// negative eigenvalues set to zero
negative = false;
for (int i = 0; i < size; ++i)
{
diagonal[i, i] = Math.Sqrt(Math.Max(jd.eigenvalues()[i], 0.0));
if (jd.eigenvalues()[i] < 0.0)
{
negative = true;
}
}
result = jd.eigenvectors() * diagonal;
normalizePseudoRoot(matrix, result);
if (negative)
{
result = hypersphereOptimize(matrix, result, true);
}
break;
case SalvagingAlgorithm.Higham:
int maxIterations = 40;
double tol = 1e-6;
result = highamImplementation(matrix, maxIterations, tol);
result = MatrixUtilities.CholeskyDecomposition(result, true);
break;
default:
throw new Exception("unknown salvaging algorithm");
}
return(result);
}
// Optimization function for hypersphere and lower-diagonal algorithm
private static Matrix hypersphereOptimize(Matrix targetMatrix, Matrix currentRoot, bool lowerDiagonal)
{
int i, j, k, size = targetMatrix.rows();
Matrix result = new Matrix(currentRoot);
Vector variance = new Vector(size);
for (i = 0; i < size; i++)
{
variance[i] = Math.Sqrt(targetMatrix[i, i]);
}
if (lowerDiagonal)
{
Matrix approxMatrix = result * Matrix.transpose(result);
result = MatrixUtilities.CholeskyDecomposition(approxMatrix, true);
for (i = 0; i < size; i++)
{
for (j = 0; j < size; j++)
{
result[i, j] /= Math.Sqrt(approxMatrix[i, i]);
}
}
}
else
{
for (i = 0; i < size; i++)
{
for (j = 0; j < size; j++)
{
result[i, j] /= variance[i];
}
}
}
ConjugateGradient optimize = new ConjugateGradient();
EndCriteria endCriteria = new EndCriteria(100, 10, 1e-8, 1e-8, 1e-8);
HypersphereCostFunction costFunction = new HypersphereCostFunction(targetMatrix, variance, lowerDiagonal);
NoConstraint constraint = new NoConstraint();
// hypersphere vector optimization
if (lowerDiagonal)
{
Vector theta = new Vector(size * (size - 1) / 2);
const double eps = 1e-16;
for (i = 1; i < size; i++)
{
for (j = 0; j < i; j++)
{
theta[i * (i - 1) / 2 + j] = result[i, j];
if (theta[i * (i - 1) / 2 + j] > 1 - eps)
{
theta[i * (i - 1) / 2 + j] = 1 - eps;
}
if (theta[i * (i - 1) / 2 + j] < -1 + eps)
{
theta[i * (i - 1) / 2 + j] = -1 + eps;
}
for (k = 0; k < j; k++)
{
theta[i * (i - 1) / 2 + j] /= Math.Sin(theta[i * (i - 1) / 2 + k]);
if (theta[i * (i - 1) / 2 + j] > 1 - eps)
{
theta[i * (i - 1) / 2 + j] = 1 - eps;
}
if (theta[i * (i - 1) / 2 + j] < -1 + eps)
{
theta[i * (i - 1) / 2 + j] = -1 + eps;
}
}
theta[i * (i - 1) / 2 + j] = Math.Acos(theta[i * (i - 1) / 2 + j]);
if (j == i - 1)
{
if (result[i, i] < 0)
{
theta[i * (i - 1) / 2 + j] = -theta[i * (i - 1) / 2 + j];
}
}
}
}
Problem p = new Problem(costFunction, constraint, theta);
optimize.minimize(p, endCriteria);
theta = p.currentValue();
result.fill(1);
for (i = 0; i < size; i++)
{
for (k = 0; k < size; k++)
{
if (k > i)
{
result[i, k] = 0;
}
else
{
for (j = 0; j <= k; j++)
{
if (j == k && k != i)
{
result[i, k] *= Math.Cos(theta[i * (i - 1) / 2 + j]);
}
else if (j != i)
{
result[i, k] *= Math.Sin(theta[i * (i - 1) / 2 + j]);
}
}
}
}
}
}
else
{
Vector theta = new Vector(size * (size - 1));
const double eps = 1e-16;
for (i = 0; i < size; i++)
{
for (j = 0; j < size - 1; j++)
{
theta[j * size + i] = result[i, j];
if (theta[j * size + i] > 1 - eps)
{
theta[j * size + i] = 1 - eps;
}
if (theta[j * size + i] < -1 + eps)
{
theta[j * size + i] = -1 + eps;
}
for (k = 0; k < j; k++)
{
theta[j * size + i] /= Math.Sin(theta[k * size + i]);
if (theta[j * size + i] > 1 - eps)
{
theta[j * size + i] = 1 - eps;
}
if (theta[j * size + i] < -1 + eps)
{
theta[j * size + i] = -1 + eps;
}
}
theta[j * size + i] = Math.Acos(theta[j * size + i]);
if (j == size - 2)
{
if (result[i, j + 1] < 0)
{
theta[j * size + i] = -theta[j * size + i];
}
}
}
}
Problem p = new Problem(costFunction, constraint, theta);
optimize.minimize(p, endCriteria);
theta = p.currentValue();
result.fill(1);
for (i = 0; i < size; i++)
{
for (k = 0; k < size; k++)
{
for (j = 0; j <= k; j++)
{
if (j == k && k != size - 1)
{
result[i, k] *= Math.Cos(theta[j * size + i]);
}
else if (j != size - 1)
{
result[i, k] *= Math.Sin(theta[j * size + i]);
}
}
}
}
}
for (i = 0; i < size; i++)
{
for (j = 0; j < size; j++)
{
result[i, j] *= variance[i];
}
}
return(result);
}
