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Option Gamma Г
Issued on November 16 2011 par Strategies Options
The gamma of an option is the rate of change of the delta to the underlying.
The gamma Г of an option is the rate of change of the delta to the underlying, that means acceleration of the p&l due to how option value moves with respect to spot move.
Because option delta rate of change is positive to positive spot move, gamma Г is always >0 (for long call and long put). Hence it's always negative for short options.
It's easy to see that
If S2>S1, ∆(S2)>∆(S1) for calls and puts, then
Г=(∆(S2)-∆(S1))/(S2-S1)>0
I - Taylor Expansion
With small spot moves, one is able tio see that the gamma is the second derivative of an option position with respect to the underlying.
Г=∂∆/∂S
Г=∂²V/∂S²
If one takes a look at the Taylor series expansion

That means : "For $1 spot moves on the same day, option variation is delta.spot variation plus 0.5 gamma . ($1)²

II - For example:
Portfolio delta is 0.52 or 52% and gamma is 0.023
→ If the spot increases by $1, next delta would be 0.52 + 0.023 = 0.543 or 54.3%
→ If the spot decreases by $1, next delta would be 0.52 - 0.023 = 0.497 or 49.7%
IV - Gamma P&L - Part of the P&L due to gamma
On attribut au gamma, la partie du PnL, Profits and Losses, qui correspond à :
P&LΓ = 0.5 . Γ . (dS)²
Where
Γ is position's gamma
dS asset variation
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OPTIONS 101 - INDEX
OPTIONS 101 - CHAPTER I
OPTIONS 101 - CHAPTER II
OPTIONS 101 - CHAPTER III
OPTIONS 101 - CHAPTER IV
OPTIONS 101 - CHAPTER V
OPTIONS 101 - CHAPTER VI Strategies Options
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