Mathematica Asked by OO_SE on August 27, 2021
Consider a random vector {s,c}
with a bivariate normal distribution. For a vector of positive scalars {a, ß, σz}
, I’m interested in calculating (numerically) the probability
NProbability[c < (1 - CDF[NormalDistribution[ ß*(s - c), σz], a]),{s,c} [Distributed] BinormalDistribution[{μs, μc}, {σs, σc}, ρ]]
Is there a way to write this same calculation using only NIntegrate?
What I’ve done so far
I’ve tried re-writing the probability, solving for s
on one side of the inequality, and nesting the integrals:
f1[c_?NumericQ,μs_, μc_, σs_, σc_, σz_, ρ_, a_, ß_]:=NIntegrate[PDF[BinormalDistribution[{μs, μc}, {σs, σc}, ρ],{s,c}],{s, c + (a-σz*InverseCDF[NormalDistribution[],1-c])(ß)^-1,[Infinity]},]
f2[μs_, μc_, σs_, σc_, σz_, ρ_, a_, ß_]:=NIntegrate[f1[c,μs, μc, σs, σc, σz, ρ, a, ß],{c,-[Infinity],[Infinity]}]
This approach unfortunately doesn’t work because the computation gets stuck with InverseCDF[NormalDistribution[],1-c]
for c
below zero or above one.
Parameter values
The scalars and distribution parameters are not important. Here is a starting set of values that can be used for reference:
{μs, μc, σs, σc, σz, ρ, a, ß} = {.35, .5, 1.1, 1.2, 1.3, .25, 1, .5}
{μs, μc, σs, σc, σz, ρ, a, ß} =
{.35, .5, 1.1, 1.2, 1.3, .25, 1, .5} // Rationalize;
ineq = c < (1 - CDF[NormalDistribution[ß*(s - c), σz], a]) //
FullSimplify
(* 2 c < Erfc[(5 (2 + c - s))/(13 Sqrt[2])] *)
NIntegrate
is an available Method
for NProbability
NProbability[ineq,
{s, c} [Distributed]
BinormalDistribution[{μs, μc}, {σs, σc}, ρ],
WorkingPrecision -> 30,
Method -> {"NIntegrate",
{MinRecursion -> 15, MaxRecursion -> 25}}]
(* 0.419500831140737615758538073412 *)
However, the "MonteCarlo"
method does not result in warning messages.
NProbability[ineq,
{s, c} [Distributed]
BinormalDistribution[{μs, μc}, {σs, σc}, ρ],
WorkingPrecision -> 30,
Method -> {"MonteCarlo", "SamplingIncrement" -> 10^4}]
(* 0.415478873239436619718309859154930 *(
Answered by Bob Hanlon on August 27, 2021
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