-4

Okay, I have found 2 short codes that work, but I want to understand how they work. I have googled and check the links such as:

http://www.tutorialspoint.com/java/lang/math_pow.htm http://www.tutorialspoint.com/java/lang/math_sqrt.htm

But the explanation there is not clear. So in other words I wish know/understand what's going on in each line of both codes.

A) The below program fragment computes (given an integer array data) and prints the geometric mean of all the entries in data:

   double product = 1;// For example, I understand why it is 1, since if it was 0 then the product would be keep getting 0, since any number *0 is always zero.
    for(int i=0; i<data.length; i++)//okay for loop is getting out all the intergers from the data array.
    product*=data[i];//This is I am not too sure, I guess each item in array is getting multiplied with each other????
    double gmean=Math.pow(product,1.0/data.length); // Yes, I hate this line, because I don't understand it, can someone explain this line please? Please use easy English, I am not as smart as you.

B) This second code fragment computes (given an integer array data) and prints the quadratic mean of all the entries in data:

double sum=0; //Okay the sum should be 0 because at the moment nothing has been summed up.
for(int i=0; i<data.length; i++)// Now getting out all the items in array called data.
sum+= data[i]*data[i];//Now I am not too sure, all the items in the array called data is getting multiplied with each other and then getting added up? I am not too sure, if would be good if someone could explain this with easy English.
double qmean = Math.sqrt(sum/data.length);// I hate this line, because I don't understand it.
System.out.println(qmean);// Displays the final result.

Okay as you can see, I do understand some lines in the code, while there are some lines, I didn't understand, it would be so fantastic if someone could explain the lines, I didn't really understand using easy English and not in a complicated way.

Thanks in advance.

Acemi
  • 173
  • 1
  • 4
  • 13
  • 4
    That's just simple math, translating the formulas for [geometric mean](http://en.wikipedia.org/wiki/Geometric_mean) and [quadratic mean](http://en.wikipedia.org/wiki/Root_mean_square) (RMS) into Java code. – NullUserException May 01 '14 at 20:20
  • You already acknowledged that the first code determines the geometric mean and second determines quadratic mean. – Engineer2021 May 01 '14 at 20:22
  • @ NullUserException, thank you for your answer, but you see, I am not as smart as you, while you find it simple, I find it as freaking difficult, I have got difficulties to understand certain lines in the code, this is the reason why I have kindly asked whether someone is able to explain the lines (I didn't understand) one by one, since this is the only thing that helps me. – Acemi May 01 '14 at 20:23
  • 2
    @Acemi I don't mean to be condescending; but if you know what the formulas for the means are, then understanding the code should be pretty straightforward. – NullUserException May 01 '14 at 20:25
  • Have you looked at Math api? The methods really dont do anything that the name doesnt tell you – Zavior May 01 '14 at 20:34

2 Answers2

1

Suppose data is {3,2,7}. data.length is 3. This will compute sqrt((9+4+49)/3).

double sum=0;
// sum is now zero

for(int i=0; i<data.length; i++)
// Execute the following statement with i having each value starting from 0,
// incrementing by 1 each time (i++), as long as i remains less than 3.
    sum+= data[i]*data[i];
    // The sum+= statement is executed three times, with i each of 0, 1, and 2.
    // The first time adds 9 to sum getting 9
    // The second time adds 4 to sum getting 13
    // The third time adds 49 to sum, getting 62

double qmean = Math.sqrt(sum/data.length);
// make qmean equal to sqrt(62/3).

System.out.println(qmean);// Displays the final result.
Patricia Shanahan
  • 25,849
  • 4
  • 38
  • 75
0

math.pow(a,b) means a^b and math.sqrt(a) is the square root of a. you don't understand the java method or the mathematical logic in your content?

Izu
  • 235
  • 1
  • 5
  • 1
    in your content its just: double gmean=Math.pow(product,1.0/data.length); = product ^ (1/data.length) its just the mathematic java code for the potency of a number – Izu May 01 '14 at 20:32
  • 1
    and double qmean = Math.sqrt(sum/data.length); is the "data.length" square root of the sum – Izu May 01 '14 at 20:35
  • can we say so, that these codes are actually like cooking recipe ? Also how do I modify these both codes if I want to check data[]={1,2,3} these 3 integers for both codes? – Acemi May 01 '14 at 20:39
  • Note that "2^3" in this answer represents "2" with "3" as a superscript. "^" is also the Java exclusive-or operator, but that is not how it is being used here. – Patricia Shanahan May 01 '14 at 20:46