var

Computes the variance of a slice.

auto var(S slice, bool isPopulation)
template var(sumTemplateArgs...)
nothrow @nogc deprecated pure nothrow @nogc
auto
var
(
S
)
(
S slice
,
bool isPopulation = true
)
if (
isSlice!S
)
auto var(S slice, Seed seed, bool isPopulation)

Members

Functions

var deprecated auto var(S slice, bool isPopulation)
var deprecated auto var(S slice, Seed seed, bool isPopulation): Undocumented in source. Be warned that the author may not have intended to support it.

Parameters

sumTemplateArgs: template arguments to pass to mir.math.sum (to compute the mean & variance of the slice)
TODO: merge fast implementation in https://github.com/libmir/numir/pull/22#issuecomment-366526194

Examples

Variance of vector

import std.math : approxEqual;
import mir.ndslice.slice : sliced;

static immutable x = [0.0, 1.0, 1.5, 2.0, 3.5, 4.25,
                      2.0, 7.5, 5.0, 1.0, 1.5, 0.0];

assert(approxEqual(x.sliced.var, 54.76563 / 12));
assert(approxEqual(x.sliced.var(false), 54.76563 / 11));
assert(approxEqual(x.sliced.var(true), 54.76563 / 12));

Variance of matrix

import mir.ndslice.slice : sliced;
import std.math : approxEqual;

static immutable x = [0.0, 1.0, 1.5, 2.0, 3.5, 4.25,
                      2.0, 7.5, 5.0, 1.0, 1.5, 0.0];

assert(approxEqual(x.sliced(2, 6).var, 54.76563 / 12));
assert(approxEqual(x.sliced(2, 6).var(false), 54.76563 / 11));
assert(approxEqual(x.sliced(2, 6).var(true), 54.76563 / 12));

Row variance of matrix

import mir.ndslice.slice : sliced;
import mir.ndslice.topology : alongDim, byDim, map;
import numir : approxEqual;

static immutable x = [0.0, 1.0, 1.5, 2.0, 3.5, 4.25,
                      2.0, 7.5, 5.0, 1.0, 1.5, 0.0];
static immutable y = [2.092014, 6.722222];

// Use byDim or alongDim with map to compute variance of row/column.
assert(approxEqual(x.sliced(2, 6).byDim!0.map!(a => a.var(true)), y.sliced));
assert(approxEqual(x.sliced(2, 6).alongDim!1.map!(a => a.var(true)), y.sliced));

Compute variance tensors along specified dimention of tensors with the negative dim support

import mir.ndslice : alongDim, iota, map, as;
import numir : var;
/*
  [[1, 2],
   [3, 4]]
 */
auto x = iota([2, 2], 1).as!double;
static immutable v0 = [1.0, 1.0];
static immutable v1 = [0.25, 0.25];
/*
  [[1, 2, 3],
   [4, 5, 6]]
 */
auto y = iota([2, 3], 1).as!double;
static immutable v2 = [2.25, 2.25, 2.25];
// static foreach (faster; [true, false])
{
    assert(x.alongDim!0.map!var == v0);
    assert(x.alongDim!(-2).map!var == v0);

    assert(x.alongDim!1.map!var == v1);
    assert(x.alongDim!(-1).map!var == v1);

    assert(y.alongDim!0.map!var == v2);
    assert(y.alongDim!(-2).map!var == v2);
}

var

Members

Functions

Parameters

Examples

See Also

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