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I have a few problem with my derivative because it shows me an error when I approach Denominator to zero .
func derivativeOf(fn: (Double) -> Double, atX x: Double) -> Double {
let h -> 0
return (fn(x + h) - fn(x))/h
}
i know my syntax sucks but currently it is common in calculus and mathematical Differential.
You can't express "number approaching zero" as let h -> 0 - this is just an invalid syntax in Swift.
There's also no specific operator for "number approaching zero". But depending on what you need, you could for example express "smallest possible positive number", using Double.leastNonzeroMagnitude:
let h = Double.leastNonzeroMagnitude
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I want to check if a variable is already defined/exists in scala or not. Lets say a function called checkVar do this operation:
var x = 10
checkVar(x) -> returns boolean True
checkVar(y) -> returns boolean False
I am asking this question because I want to create a mechanism to define a variable if it doesn't exist.
Variables only exist at compile time so you can't dynamically create or delete variables at runtime. So both x and y must be defined at compile time or else the compiler will reject the code.
What you can do is use Option to indicate whether a variable has a value or not:
def checkVar(v: Option[Int]) = v.nonEmpty
var x = Some(10)
checkVar(x) // True
val y = None
checkVar(y) // False
x = None
checkVar(x) // False
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I want to compute the square of mean-square for each element of l
l=[0.02817088, -0.74100320, -0.54062120, -0.24612808, 0.06945337, -0.58415690, -0.51238549,
-0.07862326, -0.42417337, -0.33482340, -0.21339753, -0.03890844, -0.59325371, 0.28154593,
-0.32133359,-0.13534792, 0.14060645, 0.32204972, 0.44438052, -0.21750973,-0.59107599,
-0.60809913]'
k= -0.2224834
sum(l-k)^2/22
I am not sure if sum(l-k)^2/22 is the sum of each (l[j]-k) for j=1,2,...,22?
ans = 2.4223e-14
I guess what you need might be
>> mean((l-k).^2)
ans = 0.10945
Data (You need ... for line continuation if you have data in different lines for l)
l=[0.02817088, -0.74100320, -0.54062120, -0.24612808, 0.06945337, -0.58415690, -0.51238549, ...
-0.07862326, -0.42417337, -0.33482340, -0.21339753, -0.03890844, -0.59325371, 0.28154593, ...
-0.32133359,-0.13534792, 0.14060645, 0.32204972, 0.44438052, -0.21750973,-0.59107599, ...
-0.60809913]'
k= -0.2224834
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In my while statement, I cannot understand why my output is printed twice ?
I would like to print i only one time, where is my error ?
func fetch2(){
var i: Int = 0
while i <= (self.returned-1) {
let itemLookUp = "https://shopping.yahooapis.jp/ShoppingWebService/V1/json/itemLookup?appid=\(self.appId)&itemcode=\(self.arrayCodeProduct[i])&responsegroup=large"
print(i)
i = i+1
}
}
Here is the output that I obtain :
0
1
2
3
0
1
2
3
Thank you in advance.
It looks like fetch2() is called twice.
Add a print(#function) before you var i and check that fetch2() is not called several times.
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I am struggling to see if there is an obvious advantage over which method to use when passing values into a function. My code below may not be the best example to explain the decision I'm trying to make, but it is, in my opinion, the easiest to understand.
Variadic Parameter Approach
func arithmeticMean(numbers: Double...) -> Double {
var total: Double = 0
for value in numbers {
total += value
}
return total / Double(numbers.count)
}
arithmeticMean(5, 10, 15)
Array Parameter Approach
func arithmeticMean(numbers: [Double]) -> Double {
var total: Double = 0
for value in numbers {
total += value
}
return total / Double(numbers.count)
}
arithmeticMean([5, 10, 15])
Is either of the two techniques preferred? If so, why (speed, reliability or just ease of reading)? Thanks.
I think there is no speed difference.Because,inside the function,you use Variadic Parameter just as Array.
I think that if the parameters count is small,for example,less than 5,Variadic Parameter may be a better solution,because it is easy to read.
If the count of parameters is large. Array is better solution.
Also know that,Variadic Parameter have some limitation:
A function may have at most one variadic parameter, and it must always appear last in the parameter list, to avoid ambiguity when calling the function with multiple parameters.
If your function has one or more parameters with a default value, and also has a variadic parameter, place the variadic parameter after all the defaulted parameters at the very end of the list.
Just from my idea.Hopes helpful
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For below loop and inner loop to express the performance in big o notation is :
O(N squared) as its performance is proportional to the square of the size of the input data set.
var counter = 0
var counterval = 0;
for ((key, value) <- m2.par){
for ((key2, value2) <- m2.par){
counter = counter + 1;
println(counter)
}
println(counterval)
}
Is this correct ?
Yes, if you consider the size of m2 to be the input size and that increasing counter and printing it are both O(1) (which is a very reasonable assumption).