Append nonzero entries in increasing index order; repeatedly calling
setElement would unnecessarily rescan earlier entries and could make construction quadratic.def makeVector(elems: Array[Double]): Node = {
require(elems != null)
val head = makeZeroVector(elems.length)
var tail = head
var i = 0
while (i < elems.length) {
val v = elems(i)
require(!v.isNaN && !v.isInfinity)
if (v != 0.0) {
val fresh = new Node(v, i, tail, head)
tail.next = fresh
head.prev = fresh
tail = fresh
}
i += 1
}
head
}The loop invariant says that the list represents exactly the nonzero entries of the processed input prefix, in their original coordinate order, and
tail is the final node or the header when none exist. Every append preserves the cycle and ordering. At exit, all input coordinates have their intended values. Construction takes time and data nodes, where is the array length and the number of nonzeros, plus one header. The input array is unchanged. Articles by others on the same topic
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