// NewProposalNormal constructs a new ProposalNormal for use as a proposal
// distribution for Metropolis-Hastings. ProposalNormal is a multivariate normal
// distribution (implemented by distmv.Normal) where the covariance matrix is fixed
// and the mean of the distribution changes.
//
// NewProposalNormal returns {nil, false} if the covariance matrix is not positive-definite.
func NewProposalNormal(sigma *mat64.SymDense, src *rand.Rand) (*ProposalNormal, bool) {
mu := make([]float64, sigma.Symmetric())
normal, ok := distmv.NewNormal(mu, sigma, src)
if !ok {
return nil, false
}
p := &ProposalNormal{
normal: normal,
}
return p, true
}
// CovarianceMatrix returns the covariance matrix of the distribution. Upon
// return, the value at element {i, j} of the covariance matrix is equal to
// the covariance of the i^th and j^th variables.
// covariance(i, j) = E[(x_i - E[x_i])(x_j - E[x_j])]
// If the input matrix is nil a new matrix is allocated, otherwise the result
// is stored in-place into the input.
func (n *Normal) CovarianceMatrix(s *mat64.SymDense) *mat64.SymDense {
if s == nil {
s = mat64.NewSymDense(n.Dim(), nil)
}
sn := s.Symmetric()
if sn != n.Dim() {
panic("normal: input matrix size mismatch")
}
n.setSigma()
s.CopySym(n.sigma)
return s
}
// CovarianceMatrix calculates a covariance matrix (also known as a
// variance-covariance matrix) from a matrix of data, using a two-pass
// algorithm.
//
// The weights must have length equal to the number of rows in
// input data matrix x. If cov is nil, then a new matrix with appropriate size will
// be constructed. If cov is not nil, it should have the same number of columns as the
// input data matrix x, and it will be used as the destination for the covariance
// data. Weights must not be negative.
func CovarianceMatrix(cov *mat64.SymDense, x mat64.Matrix, weights []float64) *mat64.SymDense {
// This is the matrix version of the two-pass algorithm. It doesn't use the
// additional floating point error correction that the Covariance function uses
// to reduce the impact of rounding during centering.
r, c := x.Dims()
if cov == nil {
cov = mat64.NewSymDense(c, nil)
} else if n := cov.Symmetric(); n != c {
panic(matrix.ErrShape)
}
var xt mat64.Dense
xt.Clone(x.T())
// Subtract the mean of each of the columns.
for i := 0; i < c; i++ {
v := xt.RawRowView(i)
// This will panic with ErrShape if len(weights) != len(v), so
// we don't have to check the size later.
mean := Mean(v, weights)
floats.AddConst(-mean, v)
}
if weights == nil {
// Calculate the normalization factor
// scaled by the sample size.
cov.SymOuterK(1/(float64(r)-1), &xt)
return cov
}
// Multiply by the sqrt of the weights, so that multiplication is symmetric.
sqrtwts := make([]float64, r)
for i, w := range weights {
if w < 0 {
panic("stat: negative covariance matrix weights")
}
sqrtwts[i] = math.Sqrt(w)
}
// Weight the rows.
for i := 0; i < c; i++ {
v := xt.RawRowView(i)
floats.Mul(v, sqrtwts)
}
// Calculate the normalization factor
// scaled by the weighted sample size.
cov.SymOuterK(1/(floats.Sum(weights)-1), &xt)
return cov
}
func (gp *GP) setKernelMat(s *mat64.SymDense, noise float64) {
n := s.Symmetric()
for i := 0; i < n; i++ {
for j := i; j < n; j++ {
v := gp.kernel.Distance(
gp.inputs.RawRowView(i),
gp.inputs.RawRowView(j),
)
if i == j {
v += noise
}
s.SetSym(i, j, v)
}
}
}
func (BrownBadlyScaled) Hess(x []float64, hess *mat64.SymDense) {
if len(x) != 2 {
panic("dimension of the problem must be 2")
}
if len(x) != hess.Symmetric() {
panic("incorrect size of the Hessian")
}
h00 := 2 + 2*x[1]*x[1]
h01 := 4*x[0]*x[1] - 4
h11 := 2 + 2*x[0]*x[0]
hess.SetSym(0, 0, h00)
hess.SetSym(0, 1, h01)
hess.SetSym(1, 1, h11)
}
// covToCorr converts a covariance matrix to a correlation matrix.
func covToCorr(c *mat64.SymDense) {
r := c.Symmetric()
s := make([]float64, r)
for i := 0; i < r; i++ {
s[i] = 1 / math.Sqrt(c.At(i, i))
}
for i, sx := range s {
// Ensure that the diagonal has exactly ones.
c.SetSym(i, i, 1)
for j := i + 1; j < r; j++ {
v := c.At(i, j)
c.SetSym(i, j, v*sx*s[j])
}
}
}
func (Watson) Hess(x []float64, hess *mat64.SymDense) {
dim := len(x)
if dim != hess.Symmetric() {
panic("incorrect size of the Hessian")
}
for j := 0; j < dim; j++ {
for k := j; k < dim; k++ {
hess.SetSym(j, k, 0)
}
}
for i := 1; i <= 29; i++ {
d1 := float64(i) / 29
d2 := 1.0
var s1 float64
for j := 1; j < dim; j++ {
s1 += float64(j) * d2 * x[j]
d2 *= d1
}
d2 = 1.0
var s2 float64
for _, v := range x {
s2 += d2 * v
d2 *= d1
}
t := s1 - s2*s2 - 1
s3 := 2 * d1 * s2
d2 = 2 / d1
th := 2 * d1 * d1 * t
for j := 0; j < dim; j++ {
v := float64(j) - s3
d3 := 1 / d1
for k := 0; k <= j; k++ {
hess.SetSym(k, j, hess.At(k, j)+d2*d3*(v*(float64(k)-s3)-th))
d3 *= d1
}
d2 *= d1
}
}
t1 := x[1] - x[0]*x[0] - 1
hess.SetSym(0, 0, hess.At(0, 0)+8*x[0]*x[0]+2-4*t1)
hess.SetSym(0, 1, hess.At(0, 1)-4*x[0])
hess.SetSym(1, 1, hess.At(1, 1)+2)
}
func (Wood) Hess(x []float64, hess *mat64.SymDense) {
if len(x) != 4 {
panic("dimension of the problem must be 4")
}
if len(x) != hess.Symmetric() {
panic("incorrect size of the Hessian")
}
hess.SetSym(0, 0, 400*(3*x[0]*x[0]-x[1])+2)
hess.SetSym(0, 1, -400*x[0])
hess.SetSym(1, 1, 220.2)
hess.SetSym(0, 2, 0)
hess.SetSym(1, 2, 0)
hess.SetSym(2, 2, 360*(3*x[2]*x[2]-x[3])+2)
hess.SetSym(0, 3, 0)
hess.SetSym(1, 3, 19.8)
hess.SetSym(2, 3, -360*x[2])
hess.SetSym(3, 3, 200.2)
}
func (PowellBadlyScaled) Hess(x []float64, hess *mat64.SymDense) {
if len(x) != 2 {
panic("dimension of the problem must be 2")
}
if len(x) != hess.Symmetric() {
panic("incorrect size of the Hessian")
}
t1 := 1e4*x[0]*x[1] - 1
s1 := math.Exp(-x[0])
s2 := math.Exp(-x[1])
t2 := s1 + s2 - 1.0001
h00 := 2 * (1e8*x[1]*x[1] + s1*(s1+t2))
h01 := 2 * (1e4*(1+2*t1) + s1*s2)
h11 := 2 * (1e8*x[0]*x[0] + s2*(s2+t2))
hess.SetSym(0, 0, h00)
hess.SetSym(0, 1, h01)
hess.SetSym(1, 1, h11)
}
func (BrownAndDennis) Hess(x []float64, hess *mat64.SymDense) {
if len(x) != 4 {
panic("dimension of the problem must be 4")
}
if len(x) != hess.Symmetric() {
panic("incorrect size of the Hessian")
}
for i := 0; i < 4; i++ {
for j := i; j < 4; j++ {
hess.SetSym(i, j, 0)
}
}
for i := 1; i <= 20; i++ {
d1 := float64(i) / 5
d2 := math.Sin(d1)
t1 := x[0] + d1*x[1] - math.Exp(d1)
t2 := x[2] + d2*x[3] - math.Cos(d1)
t := t1*t1 + t2*t2
s3 := 2 * t1 * t2
r1 := t + 2*t1*t1
r2 := t + 2*t2*t2
hess.SetSym(0, 0, hess.At(0, 0)+r1)
hess.SetSym(0, 1, hess.At(0, 1)+d1*r1)
hess.SetSym(1, 1, hess.At(1, 1)+d1*d1*r1)
hess.SetSym(0, 2, hess.At(0, 2)+s3)
hess.SetSym(1, 2, hess.At(1, 2)+d1*s3)
hess.SetSym(2, 2, hess.At(2, 2)+r2)
hess.SetSym(0, 3, hess.At(0, 3)+d2*s3)
hess.SetSym(1, 3, hess.At(1, 3)+d1*d2*s3)
hess.SetSym(2, 3, hess.At(2, 3)+d2*r2)
hess.SetSym(3, 3, hess.At(3, 3)+d2*d2*r2)
}
for i := 0; i < 4; i++ {
for j := i; j < 4; j++ {
hess.SetSym(i, j, 4*hess.At(i, j))
}
}
}
func (Beale) Hess(x []float64, hess *mat64.SymDense) {
if len(x) != 2 {
panic("dimension of the problem must be 2")
}
if len(x) != hess.Symmetric() {
panic("incorrect size of the Hessian")
}
t1 := 1 - x[1]
t2 := 1 - x[1]*x[1]
t3 := 1 - x[1]*x[1]*x[1]
f1 := 1.5 - x[1]*t1
f2 := 2.25 - x[1]*t2
f3 := 2.625 - x[1]*t3
h00 := 2 * (t1*t1 + t2*t2 + t3*t3)
h01 := 2 * (f1 + x[1]*(2*f2+3*x[1]*f3) - x[0]*(t1+x[1]*(2*t2+3*x[1]*t3)))
h11 := 2 * x[0] * (x[0] + 2*f2 + x[1]*(6*f3+x[0]*x[1]*(4+9*x[1]*x[1])))
hess.SetSym(0, 0, h00)
hess.SetSym(0, 1, h01)
hess.SetSym(1, 1, h11)
}
// NewNormalPrecision creates a new Normal distribution with the given mean and
// precision matrix (inverse of the covariance matrix). NewNormalPrecision
// panics if len(mu) is not equal to prec.Symmetric(). If the precision matrix
// is not positive-definite, NewNormalPrecision returns nil for norm and false
// for ok.
func NewNormalPrecision(mu []float64, prec *mat64.SymDense, src *rand.Rand) (norm *Normal, ok bool) {
if len(mu) == 0 {
panic(badZeroDimension)
}
dim := prec.Symmetric()
if dim != len(mu) {
panic(badSizeMismatch)
}
// TODO(btracey): Computing a matrix inverse is generally numerically instable.
// This only has to compute the inverse of a positive definite matrix, which
// is much better, but this still loses precision. It is worth considering if
// instead the precision matrix should be stored explicitly and used instead
// of the Cholesky decomposition of the covariance matrix where appropriate.
var chol mat64.Cholesky
ok = chol.Factorize(prec)
if !ok {
return nil, false
}
var sigma mat64.SymDense
sigma.InverseCholesky(&chol)
return NewNormal(mu, &sigma, src)
}