Difference between revisions of "TF ErrAna Homework"

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c.) Use ROOT to construct a histogram.  Compare the mean from ROOT with your result in part a above.
 
c.) Use ROOT to construct a histogram.  Compare the mean from ROOT with your result in part a above.
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== Variance usng Probability function==
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Given that
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: <math>\sigma^2 = \sum_{j=1}^n \left [ \left (x_j - \mu \right)^2 P(x)j) \right ]</math>
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Show that
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<math>\sum_{j=1}^n \left [ \left (x_j - \mu \right)^2 P(x_j) \right ] = \sum_{j=1}^n \left [ x_j^2 - P(x_j) \right ] - \mu^2</math>
  
 
=Probability Distributions=
 
=Probability Distributions=

Revision as of 02:36, 15 January 2010

Errors

Give examples of 5 a Systematic error.

Find 3 published examples of data which is wrongly represented.

Identify what is incorrect about it. What does it mean to be wrongly presented? A typical example is a political poll which does not identify the statistical uncertainty properly or at all.

Create a Histogram using ROOT

some commands that may interest you


root [1] TH1F *Hist1=new TH1F("Hist1","Hist1",50,-0.5,49.5);
root [2] Hist1->Fill(10);
root [3] Hist1->Draw();

You can use the above commands but you need to change the names and numbers above to receive credit. You must also add a title to the histogram which contains your full name. You will printout the histogram and hand it in with the above two problems.

Notice how the square rectangle in the histogram is centered at 10!
Notice that if you do the commands
root [2] Hist1->Fill(10);
root [3] Hist1->Draw();

the rectangle centered a 10 will reach the value of 2 on the vertical axis.

Two dice are rolled 20 times. Create a histogram to represent the 20 trials below

Trial Value
1 8
2 10
3 9
4 5
5 9
6 6
7 5
8 6
9 3
10 9
11 8
12 5
13 8
14 10
15 8
16 11
17 12
18 6
19 7
20 8

Mean and SD

Electron radius

The probability that an electron is a distance [math]r[/math] from the center of the hydrogen atom

[math]P(r) = Cr^2 \exp^{-2 \frac{r}{R}}[/math]

a.)Find the value of C

b.) Find the mean electron radius and standard deviation for an electron in a hydrogen atom

Histograms by Hand

Given the following test scores from 40 students.

Trial Value Trial Value Trial Value Trial Value
1 49 11 90 21 69 31 74
2 80 12 84 22 69 32 86
3 84 13 59 23 53 33 78
4 73 14 56 24 55 34 55
5 89 15 62 25 77 35 66
6 78 16 53 26 82 36 60
7 78 17 83 27 81 37 68
8 92 18 81 28 76 38 92
9 56 19 65 29 79 39 87
10 85 20 81 30 83 40 86

a.) calculate the mean and standard deviation

b.) construct a histogram by hand which has 10 bins centered on 10,20,...

c.) Use ROOT to construct a histogram. Compare the mean from ROOT with your result in part a above.

Variance usng Probability function

Given that

[math]\sigma^2 = \sum_{j=1}^n \left [ \left (x_j - \mu \right)^2 P(x)j) \right ][/math]

Show that

[math]\sum_{j=1}^n \left [ \left (x_j - \mu \right)^2 P(x_j) \right ] = \sum_{j=1}^n \left [ x_j^2 - P(x_j) \right ] - \mu^2[/math]

Probability Distributions

Error Propagation

[1] Forest_Error_Analysis_for_the_Physical_Sciences