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Unformatted text preview: 1 Temple University Continuous Time Finance Stochastic Calculus 2 Continuous Time Finance Brownian Motion 3 Scaled Random Walk = = = = = = nt j j n j X n t W T H X 1 j j 3 2 1 1 ) ( if 1 if 1 .... We speed up time (number of steps in any length of time) and scale the step size: 0.5 1 1.5 2 2.5 30.60.40.2 0.2 0.4 0.6 0.8 1 1.2 1.4 4 Limiting Distribution Brownian Motion t variance and zero mean with on distributi normal the to converges t at time evaluated ) t ( W walk random scaled the of on distributi the , n As 0. Fix t n s W(t)] s) Var[W(t W(t)] s) E[W(t with increments d distribute normally y identicall and t independen with : W process continuous a is motion Brownian = + = + + 5 Continuous Time Finance Stochastic Calculus 6 Theory of Integration w.r.t. (Random) Stochastic Processes (t) be the position in an asset at time t W(t) be the asset price at time t dW(t) the change in price over t+dt (t)dW(t) the change in position value over interval of time dt 7 Theory of Integration w.r.t. (Random) Stochastic Processes (t)dW(t) the change in position value ) ( ) ( : of sense make T t dW t Random variable versus Length (Lebesque measure) along xaxis 8 RiemannStieltjes Integral Lebesgue integration is a mathematical construction that extends the integral to a larger class of functions (e.g., Dirichlet function 1 Q ) extends the domains on which these functions can be defined (e.g., arbitrary probability space ) The RiemannStieltjes integral of a realvalued function f of a real variable with respect to a real function g is denoted by: Georg Riemann 1826 1866 Thomas Stieltjes 1856 1894 ) ( ) ( b a x dg x f 9 Recall . Riemann Integral Upper sum of f with respect to the partition is defined as: where M k is the supremum of f(x) in the interval [x k1 , x k ] . Lower sum of f with respect to the partition is defined as where d k is the infimum of f(x) in the interval [x k1 , x k ] . = +  = n k k k k x x M f RS 1 1 ) ( ) ( =  = n k k k k x x m f RS 1 1 ) ( ) ( The upper and lower Riemann sums converge to the same limit which we call the Riemann integral: b a dx x f ) ( 10 RiemannStieltjes Integral Upper sum of f over g with respect to the partition is defined as: where M k is the supremum of f(x) in the interval [x k1 , x k ] . Lower sum of f over g with respect to the partition is defined as where d k is the infimum of f(x) in the interval [x k1 , x k ] . = = n k k k k x g x g M g f U 1 1 )) ( ) ( ( ) , , ( = = n k k k k x g x g m g f L 1 1 )) ( ) ( ( ) , , ( Sums converge to upper Riemann Stieltjes integral : And lower Riemann Stieltjes integral : ) ( ) ( b a x dg x f ) ( ) ( b a x dg x f 11 Theory of Integration w.r.t....
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 Fall '09
 Soss
 Finance

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