RandomNumbers

If the pair falls under the curve is accepted

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Unformatted text preview: e. One draws a pair of random numbers, x, y and then compares if y is above or below the target distribution w(x). viii •  -.)/0"()"*+&,(1&2(3"'"24%'3(24',&)(/&.'*-( 5.*+(,.-*2.67%&'(589:(54-(,",7$",(6;(<&'( ="7)4''>( Figure 4: . The rejection method. If the pair falls under the curve is accepted, otherwise is rejected ;)49( 2"#"$*( 4$$"/*( ?@AB@A?( CD?EF( Example The following code produce numbers that follow P (x) = e−x for x = [0, 10]. Figure 5 shows the histogram of the numbers generated with this method. Listing 3: Rejection Method 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 % AM207 , REJECTION METHOD , SPRING 2013 % Pavlos Protopapas , Harvard University % REJECTION METHOD FOR exp ( - x ) for x = 0..10 clear ; xmin =0; xmax =10; N =10000; w = @ ( x ) exp ( - x ) ; cnt =0; k =1; while k <= N % pick uniform rand on 0..10 x = ( xmax - xmin ) * rand () + xmin ; % since e ^ x (x >0) < 1 pick uniform on 0 to 1 y = rand () ; y_val = w ( x ) ; if y < y_val ; xk ( k ) = x ; k = k + 1; end cnt = cnt +1; end ix 28 29 30 31 32 33 34 35 36 37 clf ; hold on ; h = hist ( xk , 50) ; % plot histogram hist ( xk , 50) ; x = xmin :0.1: xmax ; % normalize to first bin plot (x , h (1) * exp ( - x ) , ’r ’) xlabel ( ’x ’) legend ( ’ rejection method ’ , ’ exp ( - x ) ’) Figure 5: . Numbers generated using the rejection method for e−x . 350 300 250 200 150 100 50 0 0 1 2 3 4 x 5 x 6 7 8...
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This document was uploaded on 10/07/2013.

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