Add docstrings for accumulation methods on vectors

Fix bug in accumulate when initial value is provided since the implementation
doesn't support multidimentional arrays.

Move the accumulate methods with initial values to the end

base/multidimensional.jl

@@ -719,6 +719,27 @@ function cumsum(A::AbstractArray{T}, axis::Integer) where T
  cumsum!(out, A, axis)
 end
 
+"""
+ cumsum(x::AbstractVector)
+
+Cumulative sum a vector. See also [`cumsum!`](@ref)
+to use a preallocated output array, both for performance and to control the precision of the
+output (e.g. to avoid overflow).
+
+```jldoctest
+julia> cumsum([1, 1, 1])
+3-element Array{Int64,1}:
+ 1
+ 2
+ 3
+
+julia> cumsum([fill(1, 2) for i in 1:3])
+3-element Array{Array{Int64,1},1}:
+ [1, 1]
+ [2, 2]
+ [3, 3]
+```
+"""
 cumsum(x::AbstractVector) = cumsum(x, 1)
 
 """
@@ -728,6 +749,11 @@ Cumulative sum of `A` along a dimension, storing the result in `B`. See also [`c
 """
 cumsum!(B, A, axis::Integer) = accumulate!(+, B, A, axis)
 
+"""
+ cumsum!(y::AbstractVector, x::AbstractVector)
+
+Cumulative sum of a vector `x`, storing the result in `y`. See also [`cumsum`](@ref).
+"""
 cumsum!(y::AbstractVector, x::AbstractVector) = cumsum!(y, x, 1)
 
 """
@@ -756,6 +782,27 @@ julia> cumprod(a,2)
 """
 cumprod(A::AbstractArray, axis::Integer) = accumulate(*, A, axis)
 
+"""
+ cumprod(x::AbstractVector)
+
+Cumulative product of a vector. See also
+[`cumprod!`](@ref) to use a preallocated output array, both for performance and
+to control the precision of the output (e.g. to avoid overflow).
+
+```jldoctest
+julia> cumprod(fill(1//2, 3))
+3-element Array{Rational{Int64},1}:
+ 1//2
+ 1//4
+ 1//8
+
+julia> cumprod([fill(1//3, 2, 2) for i in 1:3])
+3-element Array{Array{Rational{Int64},2},1}:
+ Rational{Int64}[1//3 1//3; 1//3 1//3]
+ Rational{Int64}[2//9 2//9; 2//9 2//9]
+ Rational{Int64}[4//27 4//27; 4//27 4//27]
+```
+"""
 cumprod(x::AbstractVector) = cumprod(x, 1)
 
 """
@@ -766,6 +813,12 @@ See also [`cumprod`](@ref).
 """
 cumprod!(B, A, axis::Integer) = accumulate!(*, B, A, axis)
 
+"""
+ cumprod!(y::AbstractVector, x::AbstractVector)
+
+Cumulative product of a vector `x`, storing the result in `y`.
+See also [`cumprod`](@ref).
+"""
 cumprod!(y::AbstractVector, x::AbstractVector) = cumprod!(y, x, 1)
 
 """
@@ -778,83 +831,48 @@ there are specialized variants of `accumulate`, see:
 [`cumsum`](@ref), [`cumprod`](@ref)
 
 ```jldoctest
-julia> accumulate(+, [1,2,3])
-3-element Array{Int64,1}:
- 1
- 3
- 6
-
-julia> accumulate(*, [1,2,3])
-3-element Array{Int64,1}:
- 1
- 2
- 6
+julia> accumulate(+, fill(1, 3, 3), 1)
+3×3 Array{Int64,2}:
+ 1 1 1
+ 2 2 2
+ 3 3 3
+
+julia> accumulate(+, fill(1, 3, 3), 2)
+3×3 Array{Int64,2}:
+ 1 2 3
+ 1 2 3
+ 1 2 3
 ```
 """
 function accumulate(op, A, axis::Integer)
  out = similar(A, rcum_promote_type(op, eltype(A)))
  accumulate!(op, out, A, axis)
 end
 
-accumulate(op, x::AbstractVector) = accumulate(op, x, 1)
-
 """
- accumulate(op, v0, A)
+ accumulate(op, x::AbstractVector)
 
-Like `accumulate`, but using a starting element `v0`. The first entry of the result will be
-`op(v0, first(A))`.
+Cumulative operation `op` on a vector. See also
+[`accumulate!`](@ref) to use a preallocated output array, both for performance and
+to control the precision of the output (e.g. to avoid overflow). For common operations
+there are specialized variants of `accumulate`, see:
+[`cumsum`](@ref), [`cumprod`](@ref)
 
-# Examples
 ```jldoctest
-julia> accumulate(+, 100, [1,2,3])
+julia> accumulate(+, [1,2,3])
 3-element Array{Int64,1}:
- 101
- 103
- 106
+ 1
+ 3
+ 6
 
-julia> accumulate(min, 0, [1,2,-1])
+julia> accumulate(*, [1,2,3])
 3-element Array{Int64,1}:
-  0
-  0
- -1
+ 1
+ 2
+ 6
 ```
 """
-function accumulate(op, v0, A, axis::Integer)
- T = rcum_promote_type(op, typeof(v0), eltype(A))
- out = similar(A, T)
- accumulate!(op, out, v0, A, 1)
-end
-
-accumulate(op, v0, x::AbstractVector) = accumulate(op, v0, x, 1)
-
-function accumulate!(op::Op, B, A::AbstractVector, axis::Integer) where Op
- isempty(A) && return B
- v1 = first(A)
- _accumulate1!(op, B, v1, A, axis)
-end
-
-function accumulate!(op, B, v0, A::AbstractVector, axis::Integer)
- isempty(A) && return B
- v1 = op(v0, first(A))
- _accumulate1!(op, B, v1, A, axis)
-end
-
-accumulate!(op, y::AbstractVector, v0, x::AbstractVector) = accumulate!(op, y, v0, x, 1)
-
-function _accumulate1!(op, B, v1, A::AbstractVector, axis::Integer)
- axis > 0 || throw(ArgumentError("axis must be a positive integer"))
- inds = linearindices(A)
- inds == linearindices(B) || throw(DimensionMismatch("linearindices of A and B don't match"))
- axis > 1 && return copy!(B, A)
- i1 = inds[1]
- cur_val = v1
- B[i1] = cur_val
- @inbounds for i in inds[2:end]
- cur_val = op(cur_val, A[i])
- B[i] = cur_val
- end
- return B
-end
+accumulate(op, x::AbstractVector) = accumulate(op, x, 1)
 
 """
  accumulate!(op, B, A, dim)
@@ -888,7 +906,17 @@ function accumulate!(op, B, A, axis::Integer)
  return B
 end
 
-accumulate!(op, y::AbstractVector, x::AbstractVector) = accumulate!(op, y, x, 1)
+"""
+ accumulate!(op, y, x::AbstractVector)
+
+Cumulative operation `op` on a vector `x`, storing the result in `y`.
+See also [`accumulate`](@ref).
+"""
+function accumulate!(op::Op, y, x::AbstractVector) where Op
+ isempty(x) && return y
+ v1 = first(x)
+ _accumulate1!(op, y, v1, x, 1)
+end
 
 @noinline function _accumulate!(op, B, A, R1, ind, R2)
  # Copy the initial element in each 1d vector along dimension `axis`
@@ -903,6 +931,54 @@ accumulate!(op, y::AbstractVector, x::AbstractVector) = accumulate!(op, y, x, 1)
  B
 end
 
+"""
+ accumulate(op, v0, x::AbstractVector)
+
+Like `accumulate`, but using a starting element `v0`. The first entry of the result will be
+`op(v0, first(A))`.
+
+# Examples
+```jldoctest
+julia> accumulate(+, 100, [1,2,3])
+3-element Array{Int64,1}:
+ 101
+ 103
+ 106
+
+julia> accumulate(min, 0, [1,2,-1])
+3-element Array{Int64,1}:
+ 0
+ 0
+ -1
+```
+"""
+function accumulate(op, v0, x::AbstractVector)
+ T = rcum_promote_type(op, typeof(v0), eltype(x))
+ out = similar(x, T)
+ accumulate!(op, out, v0, x)
+end
+
+function accumulate!(op, y, v0, x::AbstractVector)
+ isempty(x) && return y
+ v1 = op(v0, first(x))
+ _accumulate1!(op, y, v1, x, 1)
+end
+
+function _accumulate1!(op, B, v1, A::AbstractVector, axis::Integer)
+ axis > 0 || throw(ArgumentError("axis must be a positive integer"))
+ inds = linearindices(A)
+ inds == linearindices(B) || throw(DimensionMismatch("linearindices of A and B don't match"))
+ axis > 1 && return copy!(B, A)
+ i1 = inds[1]
+ cur_val = v1
+ B[i1] = cur_val
+ @inbounds for i in inds[2:end]
+ cur_val = op(cur_val, A[i])
+ B[i] = cur_val
+ end
+ return B
+end
+
 ### from abstractarray.jl
 
 """