#Swift 4 , 41 bytes

{zip(0,ドル1ドル).map{0ドル==1ドル ?2*0ドル:max(0,ドル1ドル)}}

Test cases:

let f: ([Float], [Float]) -> [Float]
 = {zip(0,ドル1ドル).map{0ドル==1ドル ?2*0ドル:max(0,ドル1ドル)}}
let testcases: [(inputA: [Float], inputB: [Float], expected: [Float])] = [
 (
 inputA: [],
 inputB: [],
 expected: []
 ),
 (
 inputA: [1, 2, 3],
 inputB: [1, 3, 2],
 expected: [2, 3, 3]
 ),
 (
 inputA: [1, 3, 3.2, 2.3],
 inputB: [3, 1, 3.2, 2.6],
 expected: [3, 3, 6.4, 2.6]
 ),
 (
 inputA: [1,2,3,4,5,5,7,8,9,10],
 inputB: [10,9,8,7,6,5,4,3,2,1],
 expected: [10, 9, 8, 7, 6, 10, 7, 8, 9, 10]
 ),
 (
 inputA: [-3.2, -3.2, -2.4, 7, -10.1],
 inputB: [100, -3.2, 2.4, -7, -10.1],
 expected: [100, -6.4, 2.4, 7, -20.2]
 ),
]
for (caseNumber, testcase) in testcases.enumerated() {
 let actual = f(testcase.inputA, testcase.inputB)
 assert(actual == testcase.expected,
 "Testcase #\(caseNumber) \((testcase.inputA, testcase.inputB)) failed. Got \(actual), but expected \(testcase.expected)!")
 print("Testcase #\(caseNumber) passed!")
}

Swift 4 , 41 bytes

{zip(0,ドル1ドル).map{0ドル==1ドル ?2*0ドル:max(0,ドル1ドル)}}

Test cases:

let f: ([Float], [Float]) -> [Float]
 = {zip(0,ドル1ドル).map{0ドル==1ドル ?2*0ドル:max(0,ドル1ドル)}}
let testcases: [(inputA: [Float], inputB: [Float], expected: [Float])] = [
 (
 inputA: [],
 inputB: [],
 expected: []
 ),
 (
 inputA: [1, 2, 3],
 inputB: [1, 3, 2],
 expected: [2, 3, 3]
 ),
 (
 inputA: [1, 3, 3.2, 2.3],
 inputB: [3, 1, 3.2, 2.6],
 expected: [3, 3, 6.4, 2.6]
 ),
 (
 inputA: [1,2,3,4,5,5,7,8,9,10],
 inputB: [10,9,8,7,6,5,4,3,2,1],
 expected: [10, 9, 8, 7, 6, 10, 7, 8, 9, 10]
 ),
 (
 inputA: [-3.2, -3.2, -2.4, 7, -10.1],
 inputB: [100, -3.2, 2.4, -7, -10.1],
 expected: [100, -6.4, 2.4, 7, -20.2]
 ),
]
for (caseNumber, testcase) in testcases.enumerated() {
 let actual = f(testcase.inputA, testcase.inputB)
 assert(actual == testcase.expected,
 "Testcase #\(caseNumber) \((testcase.inputA, testcase.inputB)) failed. Got \(actual), but expected \(testcase.expected)!")
 print("Testcase #\(caseNumber) passed!")
}