/**
* <p>
* The condition p = 2 number of a matrix is used to measure the sensitivity of the linear
* system <b>Ax=b</b>. A value near one indicates that it is a well conditioned matrix.<br>
* <br>
* κ<sub>2</sub> = ||A||<sub>2</sub>||A<sup>-1</sup>||<sub>2</sub>
* </p>
* <p>
* This is also known as the spectral condition number.
* </p>
*
* @param A The matrix.
* @return The condition number.
*/
public static double conditionP2(DMatrixRMaj A)
{
SingularValueDecomposition_F64 <DMatrixRMaj> svd =
DecompositionFactory_DDRM.svd(A.numRows, A.numCols, false, false, true);
svd.decompose(A);
double[] singularValues = svd.getSingularValues();
int n = SingularOps_DDRM.rank(svd, UtilEjml.TEST_F64);
if (n == 0)
{
return(0);
}
double smallest = double.MaxValue;
double largest = double.MinValue;
foreach (double s in singularValues)
{
if (s < smallest)
{
smallest = s;
}
if (s > largest)
{
largest = s;
}
}
return(largest / smallest);
}
/**
* Computes a basis (the principal components) from the most dominant eigenvectors.
*
* @param numComponents Number of vectors it will use to describe the data. Typically much
* smaller than the number of elements in the input vector.
*/
public void computeBasis(int numComponents)
{
if (numComponents > A.getNumCols())
{
throw new ArgumentException("More components requested that the data's length.");
}
if (sampleIndex != A.getNumRows())
{
throw new ArgumentException("Not all the data has been added");
}
if (numComponents > sampleIndex)
{
throw new ArgumentException("More data needed to compute the desired number of components");
}
this.numComponents = numComponents;
// compute the mean of all the samples
for (int i = 0; i < A.getNumRows(); i++)
{
for (int j = 0; j < mean.Length; j++)
{
mean[j] += A.get(i, j);
}
}
for (int j = 0; j < mean.Length; j++)
{
mean[j] /= A.getNumRows();
}
// subtract the mean from the original data
for (int i = 0; i < A.getNumRows(); i++)
{
for (int j = 0; j < mean.Length; j++)
{
A.set(i, j, A.get(i, j) - mean[j]);
}
}
// Compute SVD and save time by not computing U
SingularValueDecomposition <DMatrixRMaj> svd =
DecompositionFactory_DDRM.svd(A.numRows, A.numCols, false, true, false);
if (!svd.decompose(A))
{
throw new InvalidOperationException("SVD failed");
}
V_t = svd.getV(null, true);
DMatrixRMaj W = svd.getW(null);
// Singular values are in an arbitrary order initially
SingularOps_DDRM.descendingOrder(null, false, W, V_t, true);
// strip off unneeded components and find the basis
V_t.reshape(numComponents, mean.Length, true);
}
/**
* <p>
* Computes the induced p = 2 matrix norm, which is the largest singular value.
* </p>
*
* @param A Matrix. Not modified.
* @return The norm.
*/
public static double inducedP2(DMatrixRMaj A)
{
SingularValueDecomposition_F64 <DMatrixRMaj> svd =
DecompositionFactory_DDRM.svd(A.numRows, A.numCols, false, false, true);
if (!svd.decompose(A))
{
throw new InvalidOperationException("Decomposition failed");
}
double[] singularValues = svd.getSingularValues();
// the largest singular value is the induced p2 norm
return(UtilEjml.max(singularValues, 0, singularValues.Length));
}
/**
* Computes the nullity of a matrix using the specified tolerance.
*
* @param A Matrix whose rank is to be calculated. Not modified.
* @param threshold The numerical threshold used to determine a singular value.
* @return The matrix's nullity.
*/
public static int nullity(DMatrixRMaj A, double threshold)
{
SingularValueDecomposition_F64 <DMatrixRMaj> svd =
DecompositionFactory_DDRM.svd(A.numRows, A.numCols, false, false, true);
if (svd.inputModified())
{
A = (DMatrixRMaj)A.copy();
}
if (!svd.decompose(A))
{
throw new InvalidOperationException("Decomposition failed");
}
return(SingularOps_DDRM.nullity(svd, threshold));
}
public SimpleSVD(Matrix mat, bool compact)
{
this.mat = mat;
this.is64 = mat is DMatrixRMaj;
if (is64)
{
DMatrixRMaj m = (DMatrixRMaj)mat;
svd = (SingularValueDecomposition <T>)DecompositionFactory_DDRM.svd(m.numRows, m.numCols, true, true, compact);
}
else
{
FMatrixRMaj m = (FMatrixRMaj)mat;
svd = (SingularValueDecomposition <T>)DecompositionFactory_FDRM.svd(m.numRows, m.numCols, true, true, compact);
}
if (!svd.decompose((T)mat))
{
throw new InvalidOperationException("Decomposition failed");
}
U = SimpleMatrix <T> .wrap(svd.getU(null, false));
W = SimpleMatrix <T> .wrap(svd.getW(null));
V = SimpleMatrix <T> .wrap(svd.getV(null, false));
// order singular values from largest to smallest
if (is64)
{
var um = U.getMatrix() as DMatrixRMaj;
var wm = W.getMatrix() as DMatrixRMaj;
var vm = V.getMatrix() as DMatrixRMaj;
SingularOps_DDRM.descendingOrder(um, false, wm, vm, false);
tol = SingularOps_DDRM.singularThreshold((SingularValueDecomposition_F64 <DMatrixRMaj>)svd);
}
else
{
var um = U.getMatrix() as FMatrixRMaj;
var wm = W.getMatrix() as FMatrixRMaj;
var vm = V.getMatrix() as FMatrixRMaj;
SingularOps_FDRM.descendingOrder(um, false, wm, vm, false);
tol = SingularOps_FDRM.singularThreshold((SingularValueDecomposition_F32 <FMatrixRMaj>)svd);
}
}
/**
* Creates a new solver targeted at the specified matrix size.
*
* @param maxRows The expected largest matrix it might have to process. Can be larger.
* @param maxCols The expected largest matrix it might have to process. Can be larger.
*/
public SolvePseudoInverseSvd_DDRM(int maxRows, int maxCols)
{
svd = DecompositionFactory_DDRM.svd(maxRows, maxCols, true, true, true);
}