HW 6

ARRAYS AND VECTORS IN C++

How are these lemenst distributed in rows and colums?

- the LL[2][3] specifies a matrix with two rows and three columns, so the {1, 2, 3, 4, 5, 6} is divided so it is a matrix that looks like:

1 2 3

4 5 6

Note: you can, and in some cases should, use braces to specify rows and columns. Fins a simple example on google.

- when defining a 2-dimensional array:

(example from https://www.geeksforgeeks.org/multidimensional-arrays-c-cpp/)

complicated example (w/o braces):

int x[3][4] = {0, 1 ,2 ,3 ,4 , 5 , 6 , 7 , 8 , 9 , 10 , 11}

simpler example (with braces):

int x[3][4] = {{0,1,2,3}, {4,5,6,7}, {8,9,10,11}};

this makes the array easier to index and thus easier to call an index in the array within a program

READING DATA FROM A FILE

VECTORS AND COMBINING CODE FROM DIFFERENT FILES

RANDOM NUMBERS

Try removing this and see how the result changes. What does the & do?

- 1st run: including the & symbol, 2nd run: removing the & symbol

- without the & symbol, the generator will print the same random number for each iteration - the & symbol ensures that inew can be redefined

Put a cout statement into the code that makes it print the first 10 “random” numbers it generates. Run the executable a couple of times. What do you notice? (This is why they are called pseudo-random numbers.)

- the output is the same (I ran it two more times and got the same 10 numbers) - this is because the random number generator has a set seed, so it will generate the same 10 random numbers each time

Try changing the seed (it should be odd and large). What happens then?

- the seed was changed to 2203 - the generator will still generate the same 10 numbers each time, but it will generate different numbers

Now try changing the number of times you call the random number generator from 1000 to other numbers (say, 10, 100, 100000, etc). What do you notice about the contents of the histogram?

- the contents of the histogram even out - with enough generations, the number generator will generate roughly the same number of events in each bin

CALORIMETER PROBLEM

NOTE: there is an intentional mistake in the code.

Look at the .C file. This is root code, so you will run it on the root prompt as

root -l resolutions.C

Set N=1 and run it. From this "data", what would you guess the mass of the mother particle is? And, how far would you guess the true mother mass could be from this measured value?

- From this data, the mass would appear to be ~60 GeV, but the mass should be ~91 GeV, so the measured mass is ~30 GeV from the true mass