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PDF of Lecture Notes - School of Mathematical Sciences

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1. DISTRIBUTION THEORY<br />

Solution. Observe that Z = h(X) = 1 σ X − µ σ ,<br />

( z +<br />

µ )<br />

σ<br />

⇒ f Z (z) = σf X 1<br />

= σf X (µ + σz)<br />

σ<br />

1<br />

= σ √ e (−1)<br />

2πσ<br />

2<br />

(2σ 2 ) (µ+σz−µ)2<br />

= 1 √<br />

2π<br />

e (−1)<br />

(2σ 2 ) σ2 z 2<br />

= 1 √<br />

2π<br />

e −z2 /2 = φ(z),<br />

i.e., Z ∼ N(0, 1).<br />

3. Suppose X ∼ Gamma (α, 1) and let Y = X λ , λ > 0.<br />

Find the <strong>PDF</strong> <strong>of</strong> Y .<br />

Solution. Since Y = 1 X, is a linear function, we have<br />

λ<br />

f Y (y) = λf X (λy)<br />

which is the Gamma(α, λ) <strong>PDF</strong>.<br />

= λ 1<br />

Γ(α) (λy)α−1 e −λy =<br />

λα<br />

Γ(α) yα−1 e −λy ,<br />

1.4 CDF transformation<br />

Suppose X is a continuous RV with CDF F X (x), which is increasing over the range <strong>of</strong><br />

X. If U = F X (x), then U ∼ U(0, 1).<br />

16

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