public void Matrices_Multiply_2x2()
{
Matrix left = new Matrix(
new decimal[, ]
{
{ 1, 2 },
{ 3, 4 }
});
Matrix right = new Matrix(
new decimal[, ]
{
{ 2, 0 },
{ 1, 2 }
});
Matrix result = Matrices.Multiply(
left,
right);
Assert.AreEqual(
new decimal[, ]
{
{ 4, 4 },
{ 10, 8 }
},
result.Array);
}
public void Matrices_Multiply_3x1times1x3()
{
Matrix left = new Matrix(
new decimal[, ]
{
{ 4 },
{ 5 },
{ 6 }
});
Matrix right = new Matrix(
new decimal[, ]
{
{ 1, 2, 3 }
});
Matrix result = Matrices.Multiply(
left,
right);
Assert.AreEqual(
new decimal[, ]
{
{ 4, 8, 12 },
{ 5, 10, 15 },
{ 6, 12, 18 }
},
result.Array);
}
public void Matrices_Multiply_AnotherExample()
{
Matrix left = new Matrix(
new decimal[, ]
{
{ -1 },
{ 3 },
{ -2 }
});
Matrix right = new Matrix(
new decimal[, ]
{
{ -1, 3, -2 }
});
Matrix result = Matrices.Multiply(
left,
right);
Assert.AreEqual(
new decimal[, ]
{
{ 1, -3, 2 },
{ -3, 9, -6 },
{ 2, -6, 4 }
},
result.Array);
}
public void Matrices_Multiply_1x3times3x1()
{
Matrix left = new Matrix(
new decimal[, ]
{
{ 1, 2, 3 }
});
Matrix right = new Matrix(
new decimal[, ]
{
{ 4 },
{ 5 },
{ 6 }
});
Matrix result = Matrices.Multiply(
left,
right);
Assert.AreEqual(
new decimal[, ]
{
{ 32 }
},
result.Array);
}
public void Regression_Solve_OLS_Partials()
{
// Boston dataset downloaded from http://lib.stat.cmu.edu/datasets/boston
// validating results against values from https://towardsdatascience.com/simple-and-multiple-linear-regression-in-python-c928425168f9
Matrix A = new Matrix(
new decimal[, ]
{
{ 12, -51, 4 },
{ 6, 167, -68 },
{ -4, 24, -41 }
});
// don't alter a1 or it will alter A
ColumnVector a1 = A.GetColumnVector(
0,
0,
A.Height);
decimal norm = a1.GetNorm();
// create copy of vector that can be edited
Matrix u = a1.AsMatrix();
Assert.AreEqual(
new decimal[, ]
{
{ 12 },
{ 6 },
{ -4 }
},
a1.AsMatrix().Array);
// subtract norm * e vector
// the sign is selected so it has the opposite sign of u1
decimal u1 = u[0, 0];
u[0, 0] -= Math.Sign(u1) * norm;
u.DivideBy(2);
Matrix uT = u.GetTranspose();
Matrix uuT = Matrices.Multiply(
u,
uT);
Matrix I = Matrices.GetIdentity(
uuT.Width);
uuT.MultiplyBy(
2 / norm);
Matrix H = Matrices.Subtract(
I,
uuT);
Matrix HA = Matrices.Multiply(
H,
A);
decimal[,] expected = new decimal[, ]
{
{ 6 / 7m, 3 / 7m, -2 / 7m },
{ 3 / 7m, -2 / 7m, 6 / 7m },
{ -2 / 7m, 6 / 7m, 3 / 7m }
};
Assert.AreEqual(
expected,
H.Array);
A = new Matrix(
new decimal[, ]
{
{ 4, 1, -2, 2 },
{ 1, 2, 0, 1 },
{ -2, 0, 3, -2 },
{ 2, 1, -2, -1 }
});
//Q1 = A.GetHouseholderMatrix();
//expected = new decimal[,]
// {
// {1, 0, 0, 0},
// {0, -1/3m, 2/3m, -2/3m},
// {0, 2/3m, 2/3m, 1/3m},
// {0, -2/3m, 1/3m, 2/3m}
// };
}
public void Regression_Solve_OLS()
{
Matrix A = new Matrix(
new decimal[, ]
{
{ 12, -51, 4 },
{ 6, 167, -68 },
{ -4, 24, -41 }
});
//Matrix A = new Matrix(
// new decimal[,]
// {
// {2, -2, 18},
// {2, 1, 0},
// {1, 2, 0}
// });
int iteration = 1;
Matrix H = A.GetHouseholder();
Matrix Q = H;
Matrix R = Matrices.Multiply(
H,
A);
if (iteration < A.Width)
{
// save storage space for the expanded versions of H
Matrix HFinal = H;
while (iteration < A.Width)
{
A = R.GetMinor(
startingRowIndex: iteration,
height: R.Height - iteration,
startingColumnIndex: iteration,
width: R.Width - iteration);
H = A.GetHouseholder();
// expand H to add 1's on diagonal for dropped rows/columns
for (int rowIndex = 0; rowIndex < iteration; rowIndex++)
{
for (int columnIndex = 0; columnIndex < HFinal.Width; columnIndex++)
{
if (rowIndex == columnIndex)
{
HFinal[rowIndex, columnIndex] = 1;
}
else
{
HFinal[rowIndex, columnIndex] = 0;
}
}
}
for (int rowIndex = iteration; rowIndex < HFinal.Height; rowIndex++)
{
for (int columnIndex = 0; columnIndex < iteration; columnIndex++)
{
HFinal[rowIndex, columnIndex] = 0;
}
}
for (int rowIndex = 0; rowIndex < H.Width; rowIndex++)
{
for (int columnIndex = 0; columnIndex < H.Height; columnIndex++)
{
HFinal[rowIndex + iteration, columnIndex + iteration] = H[rowIndex, columnIndex];
}
}
Q = Matrices.Multiply(
Q,
HFinal);
R = Matrices.Multiply(
HFinal,
R);
iteration++;
}
}
Matrix QR = Matrices.Multiply(
Q,
R);
//decimal[] b = new decimal[width];
//decimal b0 = 0;
//// need to loop including intercept
//for (int variableIndex = width; variableIndex >= 0; variableIndex--)
//{
// // use back substitution to drop out solved variables
// decimal substitutionSum = 0;
// for (int substituteIndex = b.Length - 1; substituteIndex > variableIndex - 1; substituteIndex--)
// {
// substitutionSum += b[substituteIndex] * QR[variableIndex, substituteIndex + 1];
// }
// // solve for next variable coefficient
// decimal coefficient = (values[variableIndex].y - substitutionSum) / QR[variableIndex, variableIndex + 1];
// if (variableIndex > 0)
// {
// b[variableIndex] = coefficient;
// }
// else
// {
// b0 = coefficient;
// }
//}
}