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Nov 7th, 2009

mean and standard deviation confused

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I am really confused by this problem. PLEASE HELP

Write a program that reads a set of floating point data values from the input. When the user indicates the end of the input, print out the count if the values, the average, and the standard deviation. The average of a data set is x1,......,xn is

t = Σxi/n

where Σx1 = x1+...+xn is the sum of the input values. The standard deviation is:

s=Math.sqrt(Σxi^2 - (1/n)*(Σxi)^2/n-1)

my professor asks me to Create a method in the class Mymath to print out the count of values, the average, and the standard deviation. Use the numerically less stable formula to find the standard deviation.

and this is what the output should be:

1
2
3
4
5
6
-1

Count of values: 6
Average: 3.50
Standard Deviation: 1.87

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kulrik

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Nov 7th, 2009

Re: mean and standard deviation confused

So which part are you confused about? Reading in the values? Calculating the formulas? The formulas are standard formulas, so if you don't get them, just look up those terms on google and you'll find plenty of explanations. Your professor didn't make those up. And to read in the values, you can make a Scanner. Test each value read in; if it is -1, stop reading in values, and do not include the -1 value in your calculations. So you'll basically be using a while loop to read in all the values, then adding them to an ArrayList<Integer>.

BestJewSinceJC

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Nov 7th, 2009

Re: mean and standard deviation confused

im just confused on how to do it. i guess i need a jump start thats all.

kulrik

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Nov 7th, 2009

Re: mean and standard deviation confused

Get the count
Calculate the sum
From the count and the sum, calculate the average.
From the average, get each deviation (error).
Square each deviation (squared error).
Add up the squares (sum of squared errors).
Divide by (count - 1) (mean squared error. count - 1 is degrees of freedom).
Take the square root.
You now have the standard deviation.

Slightly different formula/method than the one you listed, but if you do some math, I imagine you'll find that they are equivalent and will give identical results.

Last edited by VernonDozier; Nov 7th, 2009 at 3:04 pm.

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Jul 28th, 2010

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Re: mean and standard deviation confused

WRIGHT A PROGRAM IN C WHICH REQUEST SCORES STORES THEM IN AN ARRAY , THEN IT CALCULATES THE MEAN, Deviations FROM MEAN, STD DEVIATION AND THEN IT PRINTS THE THREE(MEAN, AVERAGE, DEVIATIONS, STD DEVIATION.)

WILSONOTIENO46@

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Jul 28th, 2010

Re: mean and standard deviation confused

Click to Expand / Collapse Quote originally posted by WILSONOTIENO46@ ...

WRIGHT A PROGRAM IN C WHICH REQUEST SCORES STORES THEM IN AN ARRAY , THEN IT CALCULATES THE MEAN, Deviations FROM MEAN, STD DEVIATION AND THEN IT PRINTS THE THREE(MEAN, AVERAGE, DEVIATIONS, STD DEVIATION.)

Don't yell( meaning don't use capitals) we are not DEAF.
Also start a new thread.
Also this is a java forum not a C forum.
Also post some code. Don't expect someone to give you the answer. If you don't know where to start, explain specifically what is your problem

javaAddict

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Jul 28th, 2010

Re: mean and standard deviation confused

On Nov. 7th VernonDozier has clearly and correctly indicated the steps in writing a code to calculate. Please following the instruction write your own program.

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This thread is more than three months old

No one has posted to this discussion for at least three months. Please let old threads die and do not reply to them unless you feel you have something new and valuable to contribute that absolutely must be added to make the discussion complete. Otherwise, please start a new thread in this forum instead.

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