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### 17.4 Sums and Products

Built-in Function: sum (x)
Built-in Function: sum (x, dim)
Built-in Function: sum (…, "native")
Built-in Function: sum (…, "double")
Built-in Function: sum (…, "extra")

  Sum of elements along dimension dim. If dim is omitted, it defaults to the first non-singleton dimension.

  If the optional argument `"native"` is given, then the sum is performed in the same type as the original argument, rather than in the default double type. For example:

      sum ([true, true])
         ⇒ 2
      sum ([true, true], "native")
         ⇒ true

  On the contrary, if `"double"` is given, the sum is performed in double precision even for single precision inputs.

  For double precision inputs, `"extra"` indicates that a more accurate algorithm than straightforward summation is to be used. For single precision inputs, `"extra"` is the same as `"double"`. Otherwise, `"extra"` has no effect.

  See also: cumsum, sumsq, prod.

Built-in Function: prod (x)
Built-in Function: prod (x, dim)

  Product of elements along dimension dim. If dim is omitted, it defaults to the first non-singleton dimension.

  See also: cumprod, sum.

Built-in Function: cumsum (x)
Built-in Function: cumsum (x, dim)
Built-in Function: cumsum (…, "native")
Built-in Function: cumsum (…, "double")
Built-in Function: cumsum (…, "extra")

  Cumulative sum of elements along dimension dim. If dim is omitted, it defaults to the first non-singleton dimension.

  See `sum` for an explanation of the optional parameters `"native"`, `"double"`, and `"extra"`.

  See also: sum, cumprod.

Built-in Function: cumprod (x)
Built-in Function: cumprod (x, dim)

  Cumulative product of elements along dimension dim. If dim is omitted, it defaults to the first non-singleton dimension.

  See also: prod, cumsum.

Built-in Function: sumsq (x)
Built-in Function: sumsq (x, dim)

  Sum of squares of elements along dimension dim. If dim is omitted, it defaults to the first non-singleton dimension.

  This function is conceptually equivalent to computing

      sum (x .* conj (x), dim)

  but it uses less memory and avoids calling `conj` if x is real.

  See also: sum, prod.

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