public void DetermineStatus()
{
var criteria = new List<IIterationStopCriterium<double>>
{
new FailureStopCriterium(),
new DivergenceStopCriterium(),
new IterationCountStopCriterium<double>(1)
};
var iterator = new Iterator<double>(criteria);
// First step, nothing should happen.
iterator.DetermineStatus(
0,
DenseVector.Create(3, i => 4),
DenseVector.Create(3, i => 4),
DenseVector.Create(3, i => 4));
Assert.AreEqual(IterationStatus.Continue, iterator.Status, "Incorrect status");
// Second step, should run out of iterations.
iterator.DetermineStatus(
1,
DenseVector.Create(3, i => 4),
DenseVector.Create(3, i => 4),
DenseVector.Create(3, i => 4));
Assert.AreEqual(IterationStatus.StoppedWithoutConvergence, iterator.Status, "Incorrect status");
}
public void CanSolveForRandomMatrix(int order)
{
var matrixA = MatrixLoader.GenerateRandomDenseMatrix(order, order);
var matrixB = MatrixLoader.GenerateRandomDenseMatrix(order, order);
var monitor = new Iterator<double>(new IIterationStopCriterium<double>[]
{
new IterationCountStopCriterium<double>(1000),
new ResidualStopCriterium(1e-10)
});
var solver = new TFQMR(monitor);
var matrixX = solver.Solve(matrixA, matrixB);
// The solution X row dimension is equal to the column dimension of A
Assert.AreEqual(matrixA.ColumnCount, matrixX.RowCount);
// The solution X has the same number of columns as B
Assert.AreEqual(matrixB.ColumnCount, matrixX.ColumnCount);
var matrixBReconstruct = matrixA*matrixX;
// Check the reconstruction.
for (var i = 0; i < matrixB.RowCount; i++)
{
for (var j = 0; j < matrixB.ColumnCount; j++)
{
Assert.AreEqual(matrixB[i, j], matrixBReconstruct[i, j], 1.0e-7);
}
}
}
public void CanSolveForRandomMatrix(int order)
{
var matrixA = Matrix<double>.Build.Random(order, order, 1);
var matrixB = Matrix<double>.Build.Random(order, order, 1);
var monitor = new Iterator<double>(
new IterationCountStopCriterium<double>(1000),
new ResidualStopCriterium<double>(1e-10));
var solver = new GpBiCg();
var matrixX = matrixA.SolveIterative(matrixB, solver, monitor);
// The solution X row dimension is equal to the column dimension of A
Assert.AreEqual(matrixA.ColumnCount, matrixX.RowCount);
// The solution X has the same number of columns as B
Assert.AreEqual(matrixB.ColumnCount, matrixX.ColumnCount);
var matrixBReconstruct = matrixA*matrixX;
// Check the reconstruction.
for (var i = 0; i < matrixB.RowCount; i++)
{
for (var j = 0; j < matrixB.ColumnCount; j++)
{
Assert.AreEqual(matrixB[i, j], matrixBReconstruct[i, j], 1.0e-7);
}
}
}
/// <summary>
/// Creates a default iterator with all the <see cref="IIterationStopCriterium"/> objects.
/// </summary>
/// <returns>A new <see cref="IIterator"/> object.</returns>
public static IIterator CreateDefault()
{
var iterator = new Iterator();
iterator.Add(new FailureStopCriterium());
iterator.Add(new DivergenceStopCriterium());
iterator.Add(new IterationCountStopCriterium());
iterator.Add(new ResidualStopCriterium());
return iterator;
}
public void SolveUnitMatrixAndBackMultiply()
{
// Create the identity matrix
var matrix = SparseMatrix.Identity(100);
// Create the y vector
var y = DenseVector.Create(matrix.RowCount, i => 1);
// Create an iteration monitor which will keep track of iterative convergence
var monitor = new Iterator<double>(new IIterationStopCriterium<double>[]
{
new IterationCountStopCriterium<double>(MaximumIterations),
new ResidualStopCriterium(ConvergenceBoundary),
new DivergenceStopCriterium(),
new FailureStopCriterium()
});
var solver = new TFQMR(monitor);
// Solve equation Ax = y
var x = solver.Solve(matrix, y);
// Now compare the results
Assert.IsNotNull(x, "#02");
Assert.AreEqual(y.Count, x.Count, "#03");
// Back multiply the vector
var z = matrix.Multiply(x);
// Check that the solution converged
Assert.IsTrue(monitor.HasConverged, "#04");
// Now compare the vectors
for (var i = 0; i < y.Count; i++)
{
Assert.IsTrue((y[i] - z[i]).IsSmaller(ConvergenceBoundary, 1), "#05-" + i);
}
}
public void ResetToPrecalculationState()
{
var criteria = new List<IIterationStopCriterium<double>>
{
new FailureStopCriterium(),
new DivergenceStopCriterium(),
new IterationCountStopCriterium<double>(1)
};
var iterator = new Iterator<double>(criteria);
// First step, nothing should happen.
iterator.DetermineStatus(
0,
DenseVector.Create(3, i => 4),
DenseVector.Create(3, i => 4),
DenseVector.Create(3, i => 4));
Assert.AreEqual(IterationStatus.Continue, iterator.Status, "Incorrect status");
iterator.Reset();
Assert.AreEqual(IterationStatus.Continue, iterator.Status, "Incorrect status");
Assert.AreEqual(IterationStatus.Continue, criteria[0].Status, "Incorrect status");
Assert.AreEqual(IterationStatus.Continue, criteria[1].Status, "Incorrect status");
Assert.AreEqual(IterationStatus.Continue, criteria[2].Status, "Incorrect status");
}
public void DetermineStatusWithoutStopCriteriaDoesNotThrow()
{
var iterator = new Iterator<double>();
Assert.DoesNotThrow(() => iterator.DetermineStatus(
0,
DenseVector.Create(3, i => 4),
DenseVector.Create(3, i => 5),
DenseVector.Create(3, i => 6)));
}
public void SolveUnitMatrixAndBackMultiply()
{
// Create the identity matrix
var matrix = Matrix<double>.Build.SparseIdentity(100);
// Create the y vector
var y = Vector<double>.Build.Dense(matrix.RowCount, 1);
// Create an iteration monitor which will keep track of iterative convergence
var monitor = new Iterator<double>(
new IterationCountStopCriterion<double>(MaximumIterations),
new ResidualStopCriterion<double>(ConvergenceBoundary),
new DivergenceStopCriterion<double>(),
new FailureStopCriterion<double>());
var solver = new MlkBiCgStab();
// Solve equation Ax = y
var x = matrix.SolveIterative(y, solver, monitor);
// Now compare the results
Assert.IsNotNull(x, "#02");
Assert.AreEqual(y.Count, x.Count, "#03");
// Back multiply the vector
var z = matrix.Multiply(x);
// Check that the solution converged
Assert.IsTrue(monitor.Status == IterationStatus.Converged, "#04");
// Now compare the vectors
for (var i = 0; i < y.Count; i++)
{
Assert.GreaterOrEqual(ConvergenceBoundary, Math.Abs(y[i] - z[i]), "#05-" + i);
}
}
public void CanSolveForRandomVector(int order)
{
var matrixA = Matrix<double>.Build.Random(order, order, 1);
var vectorb = Vector<double>.Build.Random(order, 1);
var monitor = new Iterator<double>(
new IterationCountStopCriterion<double>(1000),
new ResidualStopCriterion<double>(1e-10));
var solver = new MlkBiCgStab();
var resultx = matrixA.SolveIterative(vectorb, solver, monitor);
Assert.AreEqual(matrixA.ColumnCount, resultx.Count);
var matrixBReconstruct = matrixA*resultx;
// Check the reconstruction.
for (var i = 0; i < order; i++)
{
Assert.AreEqual(vectorb[i], matrixBReconstruct[i], 1e-7);
}
}
public void SolvePoissonMatrixAndBackMultiply()
{
// Create the matrix
var matrix = Matrix<double>.Build.Sparse(100, 100);
// Assemble the matrix. We assume we're solving the Poisson equation
// on a rectangular 10 x 10 grid
const int GridSize = 10;
// The pattern is:
// 0 .... 0 -1 0 0 0 0 0 0 0 0 -1 4 -1 0 0 0 0 0 0 0 0 -1 0 0 ... 0
for (var i = 0; i < matrix.RowCount; i++)
{
// Insert the first set of -1's
if (i > (GridSize - 1))
{
matrix[i, i - GridSize] = -1;
}
// Insert the second set of -1's
if (i > 0)
{
matrix[i, i - 1] = -1;
}
// Insert the centerline values
matrix[i, i] = 4;
// Insert the first trailing set of -1's
if (i < matrix.RowCount - 1)
{
matrix[i, i + 1] = -1;
}
// Insert the second trailing set of -1's
if (i < matrix.RowCount - GridSize)
{
matrix[i, i + GridSize] = -1;
}
}
// Create the y vector
var y = Vector<double>.Build.Dense(matrix.RowCount, 1);
// Create an iteration monitor which will keep track of iterative convergence
var monitor = new Iterator<double>(
new IterationCountStopCriterion<double>(MaximumIterations),
new ResidualStopCriterion<double>(ConvergenceBoundary),
new DivergenceStopCriterion<double>(),
new FailureStopCriterion<double>());
var solver = new MlkBiCgStab();
// Solve equation Ax = y
var x = matrix.SolveIterative(y, solver, monitor);
// Now compare the results
Assert.IsNotNull(x, "#02");
Assert.AreEqual(y.Count, x.Count, "#03");
// Back multiply the vector
var z = matrix.Multiply(x);
// Check that the solution converged
Assert.IsTrue(monitor.Status == IterationStatus.Converged, "#04");
// Now compare the vectors
for (var i = 0; i < y.Count; i++)
{
Assert.GreaterOrEqual(ConvergenceBoundary, Math.Abs(y[i] - z[i]), "#05-" + i);
}
}
private void InitializeSolver()
{
result = Vector<double>.Build.Dense(n * m);
Control.LinearAlgebraProvider = new OpenBlasLinearAlgebraProvider();
//Control.UseNativeMKL();
//Control.LinearAlgebraProvider = new MklLinearAlgebraProvider();
//Control.UseManaged();
var iterationCountStopCriterion = new IterationCountStopCriterion<double>(1000);
var residualStopCriterion = new ResidualStopCriterion<double>(1e-7);
monitor = new Iterator<double>(iterationCountStopCriterion, residualStopCriterion);
solver = new BiCgStab();
preconditioner = new MILU0Preconditioner();
}
/// <summary>
/// Solves the matrix equation Ax = b, where A is the coefficient matrix, b is the
/// solution vector and x is the unknown vector.
/// </summary>
/// <param name="matrix">The coefficient matrix, <c>A</c>.</param>
/// <param name="input">The solution vector, <c>b</c></param>
/// <param name="result">The result vector, <c>x</c></param>
/// <param name="iterator">The iterator to use to control when to stop iterating.</param>
/// <param name="preconditioner">The preconditioner to use for approximations.</param>
public void Solve(Matrix <double> matrix, Vector <double> input, Vector <double> result, Iterator <double> iterator, IPreconditioner <double> preconditioner)
{
if (matrix.RowCount != matrix.ColumnCount)
{
throw new ArgumentException(Resources.ArgumentMatrixSquare, "matrix");
}
if (result.Count != input.Count)
{
throw new ArgumentException(Resources.ArgumentVectorsSameLength);
}
if (iterator == null)
{
iterator = new Iterator <double>();
}
if (preconditioner == null)
{
preconditioner = new UnitPreconditioner <double>();
}
// Create a copy of the solution and result vectors so we can use them
// later on
var internalInput = input.Clone();
var internalResult = result.Clone();
foreach (var solver in _solvers)
{
// Store a reference to the solver so we can stop it.
IterationStatus status;
try
{
// Reset the iterator and pass it to the solver
iterator.Reset();
// Start the solver
solver.Item1.Solve(matrix, internalInput, internalResult, iterator, solver.Item2 ?? preconditioner);
status = iterator.Status;
}
catch (Exception)
{
// The solver broke down.
// Log a message about this
// Switch to the next preconditioner.
// Reset the solution vector to the previous solution
input.CopyTo(internalInput);
continue;
}
// There was no fatal breakdown so check the status
if (status == IterationStatus.Converged)
{
// We're done
internalResult.CopyTo(result);
break;
}
// We're not done
// Either:
// - calculation finished without convergence
if (status == IterationStatus.StoppedWithoutConvergence)
{
// Copy the internal result to the result vector and
// continue with the calculation.
internalResult.CopyTo(result);
}
else
{
// - calculation failed --> restart with the original vector
// - calculation diverged --> restart with the original vector
// - Some unknown status occurred --> To be safe restart.
input.CopyTo(internalInput);
}
}
}
public void DetermineStatusWithNegativeIterationNumberThrowsArgumentOutOfRangeException()
{
var criteria = new List<IIterationStopCriterium<double>>
{
new FailureStopCriterium(),
new DivergenceStopCriterium(),
new IterationCountStopCriterium<double>(),
new ResidualStopCriterium()
};
var iterator = new Iterator<double>(criteria);
Assert.Throws<ArgumentOutOfRangeException>(() => iterator.DetermineStatus(
-1,
DenseVector.Create(3, i => 4),
DenseVector.Create(3, i => 5),
DenseVector.Create(3, i => 6)));
}
public void CanSolveForRandomVector(int order)
{
var matrixA = MatrixLoader.GenerateRandomDenseMatrix(order, order);
var vectorb = MatrixLoader.GenerateRandomDenseVector(order);
var monitor = new Iterator<double>(new IIterationStopCriterium<double>[]
{
new IterationCountStopCriterium<double>(1000),
new ResidualStopCriterium(1e-10),
});
var solver = new TFQMR(monitor);
var resultx = solver.Solve(matrixA, vectorb);
Assert.AreEqual(matrixA.ColumnCount, resultx.Count);
var matrixBReconstruct = matrixA*resultx;
// Check the reconstruction.
for (var i = 0; i < order; i++)
{
Assert.AreEqual(vectorb[i], matrixBReconstruct[i], 1e-7);
}
}
public void SolvePoissonMatrixAndBackMultiply()
{
// Create the matrix
var matrix = new SparseMatrix(100);
// Assemble the matrix. We assume we're solving the Poisson equation
// on a rectangular 10 x 10 grid
const int GridSize = 10;
// The pattern is:
// 0 .... 0 -1 0 0 0 0 0 0 0 0 -1 4 -1 0 0 0 0 0 0 0 0 -1 0 0 ... 0
for (var i = 0; i < matrix.RowCount; i++)
{
// Insert the first set of -1's
if (i > (GridSize - 1))
{
matrix[i, i - GridSize] = -1;
}
// Insert the second set of -1's
if (i > 0)
{
matrix[i, i - 1] = -1;
}
// Insert the centerline values
matrix[i, i] = 4;
// Insert the first trailing set of -1's
if (i < matrix.RowCount - 1)
{
matrix[i, i + 1] = -1;
}
// Insert the second trailing set of -1's
if (i < matrix.RowCount - GridSize)
{
matrix[i, i + GridSize] = -1;
}
}
// Create the y vector
var y = DenseVector.Create(matrix.RowCount, i => 1);
// Create an iteration monitor which will keep track of iterative convergence
var monitor = new Iterator<double>(new IIterationStopCriterium<double>[]
{
new IterationCountStopCriterium<double>(MaximumIterations),
new ResidualStopCriterium(ConvergenceBoundary),
new DivergenceStopCriterium(),
new FailureStopCriterium()
});
var solver = new MlkBiCgStab(monitor);
// Solve equation Ax = y
var x = solver.Solve(matrix, y);
// Now compare the results
Assert.IsNotNull(x, "#02");
Assert.AreEqual(y.Count, x.Count, "#03");
// Back multiply the vector
var z = matrix.Multiply(x);
// Check that the solution converged
Assert.IsTrue(monitor.HasConverged, "#04");
// Now compare the vectors
for (var i = 0; i < y.Count; i++)
{
#if !PORTABLE
Assert.IsTrue(Math.Abs(y[i] - z[i]).IsSmaller(ConvergenceBoundary, 1), "#05-" + i);
#else
Assert.IsTrue(Math.Abs(y[i] - z[i]).IsSmaller(ConvergenceBoundary * 100.0, 1), "#05-" + i);
#endif
}
}
public void SolveScaledUnitMatrixAndBackMultiply()
{
// Create the identity matrix
var matrix = Matrix<double>.Build.SparseIdentity(100);
// Scale it with a funny number
matrix.Multiply(Math.PI, matrix);
// Create the y vector
var y = Vector<double>.Build.Dense(matrix.RowCount, 1);
// Create an iteration monitor which will keep track of iterative convergence
var monitor = new Iterator<double>(
new IterationCountStopCriterion<double>(MaximumIterations),
new ResidualStopCriterion<double>(ConvergenceBoundary),
new DivergenceStopCriterion<double>(),
new FailureStopCriterion<double>());
var solver = new TFQMR();
// Solve equation Ax = y
var x = matrix.SolveIterative(y, solver, monitor);
// Now compare the results
Assert.IsNotNull(x, "#02");
Assert.AreEqual(y.Count, x.Count, "#03");
// Back multiply the vector
var z = matrix.Multiply(x);
// Check that the solution converged
Assert.IsTrue(monitor.Status == IterationStatus.Converged, "#04");
// Now compare the vectors
Assert.LessOrEqual(Distance.Chebyshev(y, z), 2*ConvergenceBoundary);
}
/// <summary>
/// Run example
/// </summary>
public void Run()
{
// Format matrix output to console
var formatProvider = (CultureInfo)CultureInfo.InvariantCulture.Clone();
formatProvider.TextInfo.ListSeparator = " ";
// Solve next system of linear equations (Ax=b):
// 5*x + 2*y - 4*z = -7
// 3*x - 7*y + 6*z = 38
// 4*x + 1*y + 5*z = 43
// Create matrix "A" with coefficients
var matrixA = new DenseMatrix(new[,] { { 5.00, 2.00, -4.00 }, { 3.00, -7.00, 6.00 }, { 4.00, 1.00, 5.00 } });
Console.WriteLine(@"Matrix 'A' with coefficients");
Console.WriteLine(matrixA.ToString("#0.00\t", formatProvider));
Console.WriteLine();
// Create vector "b" with the constant terms.
var vectorB = new DenseVector(new[] { -7.0, 38.0, 43.0 });
Console.WriteLine(@"Vector 'b' with the constant terms");
Console.WriteLine(vectorB.ToString("#0.00\t", formatProvider));
Console.WriteLine();
// Create stop criteriums to monitor an iterative calculation. There are next available stop criteriums:
// - DivergenceStopCriterium: monitors an iterative calculation for signs of divergence;
// - FailureStopCriterium: monitors residuals for NaN's;
// - IterationCountStopCriterium: monitors the numbers of iteration steps;
// - ResidualStopCriterium: monitors residuals if calculation is considered converged;
// Stop calculation if 1000 iterations reached during calculation
var iterationCountStopCriterium = new IterationCountStopCriterium(1000);
// Stop calculation if residuals are below 1E-10 --> the calculation is considered converged
var residualStopCriterium = new ResidualStopCriterium(1e-10);
// Create monitor with defined stop criteriums
var monitor = new Iterator(new IIterationStopCriterium[] { iterationCountStopCriterium, residualStopCriterium });
// Load all suitable solvers from current assembly. Below in this example, there is user-defined solver
// "class UserBiCgStab : IIterativeSolverSetup<double>" which uses regular BiCgStab solver. But user may create any other solver
// and solver setup classes which implement IIterativeSolverSetup<T> and pass assembly to next function:
CompositeSolver.LoadSolverInformationFromAssembly(Assembly.GetExecutingAssembly());
// Create composite solver
var solver = new CompositeSolver(monitor);
// 1. Solve the matrix equation
var resultX = solver.Solve(matrixA, vectorB);
Console.WriteLine(@"1. Solve the matrix equation");
Console.WriteLine();
// 2. Check solver status of the iterations.
// Solver has property IterationResult which contains the status of the iteration once the calculation is finished.
// Possible values are:
// - CalculationCancelled: calculation was cancelled by the user;
// - CalculationConverged: calculation has converged to the desired convergence levels;
// - CalculationDiverged: calculation diverged;
// - CalculationFailure: calculation has failed for some reason;
// - CalculationIndetermined: calculation is indetermined, not started or stopped;
// - CalculationRunning: calculation is running and no results are yet known;
// - CalculationStoppedWithoutConvergence: calculation has been stopped due to reaching the stopping limits, but that convergence was not achieved;
Console.WriteLine(@"2. Solver status of the iterations");
Console.WriteLine(solver.IterationResult);
Console.WriteLine();
// 3. Solution result vector of the matrix equation
Console.WriteLine(@"3. Solution result vector of the matrix equation");
Console.WriteLine(resultX.ToString("#0.00\t", formatProvider));
Console.WriteLine();
// 4. Verify result. Multiply coefficient matrix "A" by result vector "x"
var reconstructVecorB = matrixA * resultX;
Console.WriteLine(@"4. Multiply coefficient matrix 'A' by result vector 'x'");
Console.WriteLine(reconstructVecorB.ToString("#0.00\t", formatProvider));
Console.WriteLine();
}
/// <summary>
/// Solves the matrix equation Ax = b, where A is the coefficient matrix, b is the
/// solution vector and x is the unknown vector.
/// </summary>
/// <param name="matrix">The coefficient matrix, <c>A</c>.</param>
/// <param name="input">The solution vector, <c>b</c></param>
/// <param name="result">The result vector, <c>x</c></param>
/// <param name="iterator">The iterator to use to control when to stop iterating.</param>
/// <param name="preconditioner">The preconditioner to use for approximations.</param>
public void Solve(Matrix <double> matrix, Vector <double> input, Vector <double> result, Iterator <double> iterator, IPreconditioner <double> preconditioner)
{
if (matrix.RowCount != matrix.ColumnCount)
{
throw new ArgumentException(Resource.ArgumentMatrixSquare, "matrix");
}
if (result.Count != input.Count)
{
throw new ArgumentException(Resource.ArgumentVectorsSameLength);
}
if (input.Count != matrix.RowCount)
{
throw Matrix.DimensionsDontMatch <ArgumentException>(input, matrix);
}
if (iterator == null)
{
iterator = new Iterator <double>();
}
if (preconditioner == null)
{
preconditioner = new UnitPreconditioner <double>();
}
preconditioner.Initialize(matrix);
var d = new DenseVector(input.Count);
var r = DenseVector.OfVector(input);
var uodd = new DenseVector(input.Count);
var ueven = new DenseVector(input.Count);
var v = new DenseVector(input.Count);
var pseudoResiduals = DenseVector.OfVector(input);
var x = new DenseVector(input.Count);
var yodd = new DenseVector(input.Count);
var yeven = DenseVector.OfVector(input);
// Temp vectors
var temp = new DenseVector(input.Count);
var temp1 = new DenseVector(input.Count);
var temp2 = new DenseVector(input.Count);
// Define the scalars
double alpha = 0;
double eta = 0;
double theta = 0;
// Initialize
var tau = input.L2Norm();
var rho = tau * tau;
// Calculate the initial values for v
// M temp = yEven
preconditioner.Approximate(yeven, temp);
// v = A temp
matrix.Multiply(temp, v);
// Set uOdd
v.CopyTo(ueven);
// Start the iteration
var iterationNumber = 0;
while (iterator.DetermineStatus(iterationNumber, result, input, pseudoResiduals) == IterationStatus.Continue)
{
// First part of the step, the even bit
if (IsEven(iterationNumber))
{
// sigma = (v, r)
var sigma = v.DotProduct(r);
if (sigma.AlmostEqualNumbersBetween(0, 1))
{
// FAIL HERE
iterator.Cancel();
break;
}
// alpha = rho / sigma
alpha = rho / sigma;
// yOdd = yEven - alpha * v
v.Multiply(-alpha, temp1);
yeven.Add(temp1, yodd);
// Solve M temp = yOdd
preconditioner.Approximate(yodd, temp);
// uOdd = A temp
matrix.Multiply(temp, uodd);
}
// The intermediate step which is equal for both even and
// odd iteration steps.
// Select the correct vector
var uinternal = IsEven(iterationNumber) ? ueven : uodd;
var yinternal = IsEven(iterationNumber) ? yeven : yodd;
// pseudoResiduals = pseudoResiduals - alpha * uOdd
uinternal.Multiply(-alpha, temp1);
pseudoResiduals.Add(temp1, temp2);
temp2.CopyTo(pseudoResiduals);
// d = yOdd + theta * theta * eta / alpha * d
d.Multiply(theta * theta * eta / alpha, temp);
yinternal.Add(temp, d);
// theta = ||pseudoResiduals||_2 / tau
theta = pseudoResiduals.L2Norm() / tau;
var c = 1 / Math.Sqrt(1 + (theta * theta));
// tau = tau * theta * c
tau *= theta * c;
// eta = c^2 * alpha
eta = c * c * alpha;
// x = x + eta * d
d.Multiply(eta, temp1);
x.Add(temp1, temp2);
temp2.CopyTo(x);
// Check convergence and see if we can bail
if (iterator.DetermineStatus(iterationNumber, result, input, pseudoResiduals) != IterationStatus.Continue)
{
// Calculate the real values
preconditioner.Approximate(x, result);
// Calculate the true residual. Use the temp vector for that
// so that we don't pollute the pseudoResidual vector for no
// good reason.
CalculateTrueResidual(matrix, temp, result, input);
// Now recheck the convergence
if (iterator.DetermineStatus(iterationNumber, result, input, temp) != IterationStatus.Continue)
{
// We're all good now.
return;
}
}
// The odd step
if (!IsEven(iterationNumber))
{
if (rho.AlmostEqualNumbersBetween(0, 1))
{
// FAIL HERE
iterator.Cancel();
break;
}
var rhoNew = pseudoResiduals.DotProduct(r);
var beta = rhoNew / rho;
// Update rho for the next loop
rho = rhoNew;
// yOdd = pseudoResiduals + beta * yOdd
yodd.Multiply(beta, temp1);
pseudoResiduals.Add(temp1, yeven);
// Solve M temp = yOdd
preconditioner.Approximate(yeven, temp);
// uOdd = A temp
matrix.Multiply(temp, ueven);
// v = uEven + beta * (uOdd + beta * v)
v.Multiply(beta, temp1);
uodd.Add(temp1, temp);
temp.Multiply(beta, temp1);
ueven.Add(temp1, v);
}
// Calculate the real values
preconditioner.Approximate(x, result);
iterationNumber++;
}
}
/// <summary>
/// Run example
/// </summary>
public void Run()
{
// Format matrix output to console
var formatProvider = (CultureInfo)CultureInfo.InvariantCulture.Clone();
formatProvider.TextInfo.ListSeparator = " ";
// Solve next system of linear equations (Ax=b):
// 5*x + 2*y - 4*z = -7
// 3*x - 7*y + 6*z = 38
// 4*x + 1*y + 5*z = 43
// Create matrix "A" with coefficients
var matrixA = DenseMatrix.OfArray(new[,] { { 5.00, 2.00, -4.00 }, { 3.00, -7.00, 6.00 }, { 4.00, 1.00, 5.00 } });
Console.WriteLine(@"Matrix 'A' with coefficients");
Console.WriteLine(matrixA.ToString("#0.00\t", formatProvider));
Console.WriteLine();
// Create vector "b" with the constant terms.
var vectorB = new DenseVector(new[] { -7.0, 38.0, 43.0 });
Console.WriteLine(@"Vector 'b' with the constant terms");
Console.WriteLine(vectorB.ToString("#0.00\t", formatProvider));
Console.WriteLine();
// Create stop criteriums to monitor an iterative calculation. There are next available stop criteriums:
// - DivergenceStopCriterium: monitors an iterative calculation for signs of divergence;
// - FailureStopCriterium: monitors residuals for NaN's;
// - IterationCountStopCriterium: monitors the numbers of iteration steps;
// - ResidualStopCriterium: monitors residuals if calculation is considered converged;
// Stop calculation if 1000 iterations reached during calculation
var iterationCountStopCriterium = new IterationCountStopCriterium<double>(1000);
// Stop calculation if residuals are below 1E-10 --> the calculation is considered converged
var residualStopCriterium = new ResidualStopCriterium(1e-10);
// Create monitor with defined stop criteriums
var monitor = new Iterator<double>(new IIterationStopCriterium<double>[] { iterationCountStopCriterium, residualStopCriterium });
// Create Transpose Free Quasi-Minimal Residual solver
var solver = new TFQMR(monitor);
// 1. Solve the matrix equation
var resultX = solver.Solve(matrixA, vectorB);
Console.WriteLine(@"1. Solve the matrix equation");
Console.WriteLine();
// 2. Check solver status of the iterations.
// Solver has property IterationResult which contains the status of the iteration once the calculation is finished.
// Possible values are:
// - CalculationCancelled: calculation was cancelled by the user;
// - CalculationConverged: calculation has converged to the desired convergence levels;
// - CalculationDiverged: calculation diverged;
// - CalculationFailure: calculation has failed for some reason;
// - CalculationIndetermined: calculation is indetermined, not started or stopped;
// - CalculationRunning: calculation is running and no results are yet known;
// - CalculationStoppedWithoutConvergence: calculation has been stopped due to reaching the stopping limits, but that convergence was not achieved;
Console.WriteLine(@"2. Solver status of the iterations");
Console.WriteLine(solver.IterationResult);
Console.WriteLine();
// 3. Solution result vector of the matrix equation
Console.WriteLine(@"3. Solution result vector of the matrix equation");
Console.WriteLine(resultX.ToString("#0.00\t", formatProvider));
Console.WriteLine();
// 4. Verify result. Multiply coefficient matrix "A" by result vector "x"
var reconstructVecorB = matrixA * resultX;
Console.WriteLine(@"4. Multiply coefficient matrix 'A' by result vector 'x'");
Console.WriteLine(reconstructVecorB.ToString("#0.00\t", formatProvider));
Console.WriteLine();
}
/// <summary>
/// Solves the matrix equation Ax = b, where A is the coefficient matrix, b is the
/// solution vector and x is the unknown vector.
/// </summary>
/// <param name="matrix">The coefficient <see cref="Matrix"/>, <c>A</c>.</param>
/// <param name="input">The solution <see cref="Vector"/>, <c>b</c>.</param>
/// <param name="result">The result <see cref="Vector"/>, <c>x</c>.</param>
/// <param name="iterator">The iterator to use to control when to stop iterating.</param>
/// <param name="preconditioner">The preconditioner to use for approximations.</param>
public void Solve(Matrix <double> matrix, Vector <double> input, Vector <double> result, Iterator <double> iterator, IPreconditioner <double> preconditioner)
{
if (matrix.RowCount != matrix.ColumnCount)
{
throw new ArgumentException(Resources.ArgumentMatrixSquare, nameof(matrix));
}
if (result.Count != input.Count)
{
throw new ArgumentException(Resources.ArgumentVectorsSameLength);
}
if (input.Count != matrix.RowCount)
{
throw Matrix.DimensionsDontMatch <ArgumentException>(input, matrix);
}
if (iterator == null)
{
iterator = new Iterator <double>();
}
if (preconditioner == null)
{
preconditioner = new UnitPreconditioner <double>();
}
preconditioner.Initialize(matrix);
// Compute r_0 = b - Ax_0 for some initial guess x_0
// In this case we take x_0 = vector
// This is basically a SAXPY so it could be made a lot faster
var residuals = new DenseVector(matrix.RowCount);
CalculateTrueResidual(matrix, residuals, result, input);
// Choose r~ (for example, r~ = r_0)
var tempResiduals = residuals.Clone();
// create seven temporary vectors needed to hold temporary
// coefficients. All vectors are mangled in each iteration.
// These are defined here to prevent stressing the garbage collector
var vecP = new DenseVector(residuals.Count);
var vecPdash = new DenseVector(residuals.Count);
var nu = new DenseVector(residuals.Count);
var vecS = new DenseVector(residuals.Count);
var vecSdash = new DenseVector(residuals.Count);
var temp = new DenseVector(residuals.Count);
var temp2 = new DenseVector(residuals.Count);
// create some temporary double variables that are needed
// to hold values in between iterations
double currentRho = 0;
double alpha = 0;
double omega = 0;
var iterationNumber = 0;
while (iterator.DetermineStatus(iterationNumber, result, input, residuals) == IterationStatus.Continue)
{
// rho_(i-1) = r~^T r_(i-1) // dotproduct r~ and r_(i-1)
var oldRho = currentRho;
currentRho = tempResiduals.DotProduct(residuals);
// if (rho_(i-1) == 0) // METHOD FAILS
// If rho is only 1 ULP from zero then we fail.
if (currentRho.AlmostEqualNumbersBetween(0, 1))
{
// Rho-type breakdown
throw new NumericalBreakdownException();
}
if (iterationNumber != 0)
{
// beta_(i-1) = (rho_(i-1)/rho_(i-2))(alpha_(i-1)/omega(i-1))
var beta = (currentRho / oldRho) * (alpha / omega);
// p_i = r_(i-1) + beta_(i-1)(p_(i-1) - omega_(i-1) * nu_(i-1))
nu.Multiply(-omega, temp);
vecP.Add(temp, temp2);
temp2.CopyTo(vecP);
vecP.Multiply(beta, vecP);
vecP.Add(residuals, temp2);
temp2.CopyTo(vecP);
}
else
{
// p_i = r_(i-1)
residuals.CopyTo(vecP);
}
// SOLVE Mp~ = p_i // M = preconditioner
preconditioner.Approximate(vecP, vecPdash);
// nu_i = Ap~
matrix.Multiply(vecPdash, nu);
// alpha_i = rho_(i-1)/ (r~^T nu_i) = rho / dotproduct(r~ and nu_i)
alpha = (currentRho * 1) / tempResiduals.DotProduct(nu);
// s = r_(i-1) - alpha_i nu_i
nu.Multiply(-alpha, temp);
residuals.Add(temp, vecS);
// Check if we're converged. If so then stop. Otherwise continue;
// Calculate the temporary result.
// Be careful not to change any of the temp vectors, except for
// temp. Others will be used in the calculation later on.
// x_i = x_(i-1) + alpha_i * p^_i + s^_i
vecPdash.Multiply(alpha, temp);
temp.Add(vecSdash, temp2);
temp2.CopyTo(temp);
temp.Add(result, temp2);
temp2.CopyTo(temp);
// Check convergence and stop if we are converged.
if (iterator.DetermineStatus(iterationNumber, temp, input, vecS) != IterationStatus.Continue)
{
temp.CopyTo(result);
// Calculate the true residual
CalculateTrueResidual(matrix, residuals, result, input);
// Now recheck the convergence
if (iterator.DetermineStatus(iterationNumber, result, input, residuals) != IterationStatus.Continue)
{
// We're all good now.
return;
}
// Continue the calculation
iterationNumber++;
continue;
}
// SOLVE Ms~ = s
preconditioner.Approximate(vecS, vecSdash);
// temp = As~
matrix.Multiply(vecSdash, temp);
// omega_i = temp^T s / temp^T temp
omega = temp.DotProduct(vecS) / temp.DotProduct(temp);
// x_i = x_(i-1) + alpha_i p^ + omega_i s^
temp.Multiply(-omega, residuals);
residuals.Add(vecS, temp2);
temp2.CopyTo(residuals);
vecSdash.Multiply(omega, temp);
result.Add(temp, temp2);
temp2.CopyTo(result);
vecPdash.Multiply(alpha, temp);
result.Add(temp, temp2);
temp2.CopyTo(result);
// for continuation it is necessary that omega_i != 0.0
// If omega is only 1 ULP from zero then we fail.
if (omega.AlmostEqualNumbersBetween(0, 1))
{
// Omega-type breakdown
throw new NumericalBreakdownException();
}
if (iterator.DetermineStatus(iterationNumber, result, input, residuals) != IterationStatus.Continue)
{
// Recalculate the residuals and go round again. This is done to ensure that
// we have the proper residuals.
// The residual calculation based on omega_i * s can be off by a factor 10. So here
// we calculate the real residual (which can be expensive) but we only do it if we're
// sufficiently close to the finish.
CalculateTrueResidual(matrix, residuals, result, input);
}
iterationNumber++;
}
}