The Power class.

Source: R/elementwise.R

This class represents the elementwise power function \(f(x) = x^p\). If expr is a CVXR expression, then expr^p is equivalent to Power(expr, p).

Power(x, p, max_denom = 1024)

# S4 method for Power
to_numeric(object, values)

# S4 method for Power
sign_from_args(object)

# S4 method for Power
is_atom_convex(object)

# S4 method for Power
is_atom_concave(object)

# S4 method for Power
is_atom_log_log_convex(object)

# S4 method for Power
is_atom_log_log_concave(object)

# S4 method for Power
is_constant(object)

# S4 method for Power
is_incr(object, idx)

# S4 method for Power
is_decr(object, idx)

# S4 method for Power
is_quadratic(object)

# S4 method for Power
is_qpwa(object)

# S4 method for Power
.grad(object, values)

# S4 method for Power
.domain(object)

# S4 method for Power
get_data(object)

# S4 method for Power
copy(object, args = NULL, id_objects = list())

# S4 method for Power
name(x)

Arguments

x

The Expression to be raised to a power.

p

A numeric value indicating the scalar power.

max_denom

The maximum denominator considered in forming a rational approximation of p.

object

A Power object.

values

A list of numeric values for the arguments

idx

An index into the atom.

args

A list of arguments to reconstruct the atom. If args=NULL, use the current args of the atom

id_objects

Currently unused.

Details

For \(p = 0\), \(f(x) = 1\), constant, positive.

For \(p = 1\), \(f(x) = x\), affine, increasing, same sign as \(x\).

For \(p = 2,4,8,...\), \(f(x) = |x|^p\), convex, signed monotonicity, positive.

For \(p < 0\) and \(f(x) = \)

\(x^p\)

for \(x > 0\)

\(+\infty\)

\(x \leq 0\)

, this function is convex, decreasing, and positive.

For \(0 < p < 1\) and \(f(x) =\)

\(x^p\)

for \(x \geq 0\)

\(-\infty\)

\(x < 0\)

, this function is concave, increasing, and positive.

For \(p > 1, p \neq 2,4,8,\ldots\) and \(f(x) = \)

\(x^p\)

for \(x \geq 0\)

\(+\infty\)

\(x < 0\)

, this function is convex, increasing, and positive.

Methods (by generic)

  • to_numeric(Power): Throw an error if the power is negative and cannot be handled.

  • sign_from_args(Power): The sign of the atom.

  • is_atom_convex(Power): Is \(p \leq 0\) or \(p \geq 1\)?

  • is_atom_concave(Power): Is \(p \geq 0\) or \(p \leq 1\)?

  • is_atom_log_log_convex(Power): Is the atom log-log convex?

  • is_atom_log_log_concave(Power): Is the atom log-log concave?

  • is_constant(Power): A logical value indicating whether the atom is constant.

  • is_incr(Power): A logical value indicating whether the atom is weakly increasing.

  • is_decr(Power): A logical value indicating whether the atom is weakly decreasing.

  • is_quadratic(Power): A logical value indicating whether the atom is quadratic.

  • is_qpwa(Power): A logical value indicating whether the atom is quadratic of piecewise affine.

  • .grad(Power): Gives the (sub/super)gradient of the atom w.r.t. each variable

  • .domain(Power): Returns constraints describng the domain of the node

  • get_data(Power): A list containing the output of pow_low, pow_mid, or pow_high depending on the input power.

  • copy(Power): Returns a shallow copy of the power atom

  • name(Power): Returns the expression in string form.

Slots

x

The Expression to be raised to a power.

p

A numeric value indicating the scalar power.

max_denom

The maximum denominator considered in forming a rational approximation of p.