how to use mutliple values calculated by a function?

Peter Gray

I have a function that calculates 10 pairs of values (x,y co-ordinates of a graph). I want to use these to calculate the area under the curve.Although I can plot the graph, I do not know how I get to use the values in the following expression:
(x10-x9)*(y10-y9)+(x9-x8)*(y9-y8)+...
Can one create an array of x,y pairs ( how?) or is there some other way to identify the output as x,y pairs to be used in the way that I wish to.
The reason why I cannot simply enter the values is that the graph changes dependent upon the distribution of another set of data which responds to a slider
I am new to this, so please be explicit in any explanation that you might give.
Many thanks

Oct 4 '10 #1

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1648

gits

5,390

Expert Mod 4TB

you might simply use nested arrays like:

Expand|Select|Wrap|Line Numbers

 var valPairs = [[1,2], [3,4], [5,6]];
 
// alerts the first pair of values

// which is an array itself

alert(valPairs[0]);

Oct 4 '10 #2

Peter Gray

The problem is that I don't know how to make the output of the function an array. I use a looped calculation for (var i=0; i<10; i++) which generates the ten or so pairs: using document.write the output of the function is this
1 1

0.98 1

0.84 1

0.5 0.94

0.16 0.7

0.02 0.31000000000000005

0.02 0.31000000000000005
I don;'t know how to use this output and identify each as an x,y pair to do the further calculation.
Thanks for your suggestions.

Oct 4 '10 #3

gits

5,390

Expert Mod 4TB

please post some code ... basically you might use something like this:

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 var valuePairs = [];
 
for (var i = 0; i < 10; i++) {

    valuePairs.push([i, i + 1]);

}

which will produce the following array:

Expand|Select|Wrap|Line Numbers

 [[0, 1], [1, 2], [2, 3], [3, 4], [4, 5], [5, 6], [6, 7], [7, 8], [8, 9], [9, 10]]
 

Oct 4 '10 #4

Peter Gray

Gits
Could I post directly to you perhaps. The code is a few hundred lines long and I think one is restricted to 20 lines with this forum.
Peter

Oct 4 '10 #5

Peter Gray

I made a boo boo in posting the code in the e-mail. Hope that this is correct. Not done this before. My apologies

Expand|Select|Wrap|Line Numbers

 
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<html>

 <head>

  <title> AUC calculation</title>
 
  <style type="text/css">

  p    {

  font-family:comic sans MS;

  color:blue;

  }

  th    {

  font-family:comic sans MS;

  color:#330033;

  }

  td    {

  font-family:comic saNS ms;

  COLOR:#6600cc;

  }

  </style>
 
 </head>
 
 <body >

  <p> I wonder whether I shall ever get this right? At least everything appears on the same page! And in a table too... Trouble is, I cannot make them into numbered pairs and use them in a formula.</p>

  <table border="1">

  <tr><th>x</th><th>y</th></tr>

  <script type="text/javascript">
 
    var FPF=[];

    var TPF =[];
 
    var x=-1;

    //parseFloat($('#display').val());//1;//slider_form.elements["display"].value;//slider_form.elements.display.value;// slider value

    var LT = parseFloat(-3 + (0.8571 *x));//changes slider value to the left tail value 'with disease'

    var RT= 3;//value for right tail of 'without disease'

    var c= parseFloat(1.739 + (0.6116*x)+(0.01297*x*Math.exp(2))-(0.01142*x*Math.exp(3))-(0.004572*x*Math.exp(4))); //intersect between two curves
 
//from Stephen Whitney application 25yearsofprogramming.com 'probability.js'

 function NormalDensityZx(x, Mean, StdDev)

{

    var a = x - Mean;

    return Math.exp(-(a * a) / (2 * StdDev * StdDev)) / (Math.sqrt(2 * Math.PI) * StdDev); 

}
 
//----------------------------------------------------------------------------------------------

// Calculates Q(x), the right tail area under the Standard Normal Curve. 

function StandardNormalQx(x)

{

    x = i;

    if(x === 0)    // no approximation necessary for 0

        return 0.50;
 
    var t1,t2,t3,t4,t5,qx;

    var negative = false;

    if(x < 0)

    {

        x = -x;

        negative = true;

    }

    t1 = 1/(1 + (0.2316419 * x)); 

    t2 = t1 * t1; 

    t3 = t2 * t1; 

    t4 = t3 * t1; 

    t5 = t4 * t1;

    qx = NormalDensityZx(x,0,1) * ((0.319381530 * t1) + (-0.356563782 * t2) + 

                                (1.781477937 * t3) + (-1.821255978 * t4) + (1.330274429 * t5));

    if(negative == true)

        qx = 1 - qx;

    return qx;

}
 
//----------------------------------------------------------------------------------------------

// Calculates P(x), the left tail area under the Standard Normal Curve, which is 1 - Q(x). 

function StandardNormalPx(x)

{
 
    x = -2.8+(i-LT);

    if(x === 0)    // no approximation necessary for 0

        return 0.50;
 
    var t1,t2,t3,t4,t5,qx;

    var negative = false;

    if(x < 0)

    {

        x = -x;

        negative = true;

    }

    t1 = 1/(1 + (0.2316419 * x)); 

    t2 = t1 * t1; 

    t3 = t2 * t1; 

    t4 = t3 * t1; 

    t5 = t4 * t1;

    qx = NormalDensityZx(x,0,1) * ((0.319381530 * t1) + (-0.356563782 * t2) + 

                                (1.781477937 * t3) + (-1.821255978 * t4) + (1.330274429 * t5));

    if(negative == true)

        qx = 1 - qx;
 
    return 1 - qx;
 
}

//end Stephen Whitney probability.js
 
//calculate points for ROC plot from -3 to +3 at unit intervals    

var valuePairs=[FPF,TPF];

for (var i =-3; i<3.1; i++ ){
 
if (i<LT){
 
            PQAQX = (StandardNormalQx(x).toFixed(2)); //AUC false positives based on AUC = 1

            FPF =parseFloat(StandardNormalQx(x).toFixed(2));

            TPF = 1;}
 
else if (i>LT && i<RT){
 
PQAQX= (StandardNormalQx(x).toFixed(2));

PQAPX= (StandardNormalPx(x).toFixed(2));
 
TPF = (1-StandardNormalPx(x).toFixed(2));

FPF = parseFloat(StandardNormalQx(x).toFixed(2));

}
 
else if (i >3.01){
 
PQAPX= (StandardNormalPx(x).toFixed(2));

TPF = (1-StandardNormalPx(x).toFixed(2));

FPF = 1;

        }

         valuePairs.push([i, i + 1]); 

        //var xArray = new Array(FPF.toFixed(2));

        //var yArray = new Array(TPF.toFixed(2));
 
        //document.writeln('<tr><td>'+(xArray[0])+'</td><td>'+(yArray[0])+'</td></tr>');
 
        //calculate area under the curve

        //take x and y values from function and do AUC calculation

        //var G1= 1-Math.sum((x-x)*(y-y)); this function does not exist! description only

        //var AUC= (G1 + 1)/2;

        //var d=AUC-0.5;

        }

        </script>

        </table>

 </body>

</html>

Oct 4 '10 #6

gits

5,390

Expert Mod 4TB

so what is your desired output and how do you want to process the values later on ...

Oct 7 '10 #7

peter gray

I want to take the values from line 137 ( the function that finishes line 132 and then use these results in the calculation described on line 142. So I need to be able to extract x1, subract x2 from it, multiply the difference between y1 and y2 and then add this number to the difference between x2 and x3 multiplied by the difference between y2 and y3 and so on to the end of the array. My problem is that I cannot extract particular numbers from the array. I have tried x[0], x[0][0], but this just gives 'undefined'
THe generic description of the calulation would be:
the sum of (xn-xn-1)*(yn-yn-1)from the first x,y pair to the last x,y pair

Oct 7 '10 #8

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