Questions tagged [copula]
A copula is a multivariate distribution with uniform marginal distributions. Copulas are mostly used to represent/model the structure of dependence between random variables, separately from the margins.
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Copula models and the distribution of the sum of random variables without Monte Carlo
There is a vast literature on copula modelling. Using copulas I can describe the joint law of two (and more) random variables $X$ and $Y$, i.e. $F_{X,Y}(x,y)$.
Very often in risk management (credit ...
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Copulas simply explained
I try to understand the basic idea of copulas, however I am still struggling and hope that someone can help me.
I understood that in general a copula is a function which links several marginal ...
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copula-marginal algorithm
has there been any interesting work or advances on the copula-marginal algorithm (CMA) as proposed by
Attilio Meucci. I am unable to find anything on the web other then the original article, here is ...
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Copula Correlations
It seems that the sample linear correlation coefficient $\hat{\rho}$ of samples generated by a copula that is parametrized by $\rho$ is unequal to $\rho$. For example, I construct a Normal copula with ...
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Simulating from a multivariate clayton copula
I am recently into copulas for finance, I've read several examples of how to generate dependent random variables with most kind of copulas. The problem for me is that all the books describe the case ...
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Fitting Copula and Simulation
I would greatly appreciate any insights into the problem described below,
regarding using the data obtained from applying the functions of the
rugarch package ...
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Portfolio VaR with Copula?
Let the portfolio be given by:
$$X=X_1+X_2$$
$(X_1,X_2)$ are dependent through a Copula function $C(u_1,u_2)$, such that the joint distribution is given by:
$$F(x_1,x_2)=C(F(x_1),F(x_2))$$
What is ...
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Is there a copula that can estimate negative tail dependence?
I have encountered numerous copula estimators that can estimate time-invariant and time-varying linear and non-linear correlations on the interval $[-1,1]$, and these estimators are fully consistent ...
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Generate correlated random variables from Normal and Gamma distributions
I want to generate a random vector $z$ of dimension $k+m$ with some given correlation matrix $\Sigma$, such that the first $k$ elements of the vector are distributed normally and the last $m$ elements ...
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How to price this basket option?
Underlying assets are three global stock index : Eurostoxx 50, HSI, KOSPI 200
Maturity: 36 months with advanced redemption date in every 6 months if prices of indexes satisfy given conditions at each ...
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Why do we not use copula for forward starting options?
Why do we use copulas for spread options but do not use them to correlate random variables across time, such as in the forward starting option?
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Simulate (imaginary) asset prices using random numbers that follow a Frank Copula
I didn't understand how to simulate asset prices by using non normal random numbers.
I am assuming that it would be incorrect to use the standard Geometric Brownian Motion, since it is based solely ...
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Difference between Local Vol and Copula
Let's assume we have ATM European call on a basket of two stocks and price it with:
1) Multivariate Local Vol with constant correlation
2) Gaussian copula
Assuming we use the same correlation ...
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Estimation of ranks of log-returns via copula
I have successfully chosen and estimate a copula for the ranks of the log-returns of my actions. My question is, since I have worked with the ranks instead of directly the log-returns (in order to be ...
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Do I need a copula to accurately estimate the VaR of a portfolio of risky assets?
I need to estimate the daily VaR of a portfolio of various exposures in $n$ risky assets (say equity futures).
The simplest approach, I think, would be to just estimate VaR from a multivariate normal ...
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Convolution copula?
Using copula formulation for the following probability:
$$\mathbb{P}(X\leq x,y_{1}\leq Y\leq y_{2})=\mathbb{P}(X\leq x,Y\leq y_{2})-\mathbb{P}(X\leq x,Y\leq y_{1})$$
$$=C(F_{X}(x),F_{Y}(y_{2}))-C(F_{...
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Ito integrals and copulas
Let $X_{t}$ and $Y_{t}$ be two brownian motions and let their joint distribution be given by $F$. So in regularly correlated BM's where $dX_{t}dY_{t}=\rho dt$, we have a bivariate normal distribution ...
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Metric for measuring the "spread" of a copula
I am fitting copula to log returns data for my undergraduate thesis, and comparing the quality of the fit with AIC. One interesting thing that I found is that the Clayton copula, which has negative ...
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How can we compute copula functions by using Fast Fourier transformation?
Q1. If a copula is expressed in terms of its moment generating function then how can this copula can be computed by using Fast Fourier Transformation?
Q2. Can we use copula to evaluate spread option ...
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Is non-stationarity an issue during copula estimation?
In this paper (1), on page 14 (section 4), the author presents an empirical experiment on the computation of a copula through the use of kernels. To do so, he uses the following stochastic process (...
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Any video lecture on copula function, a statistics concept for measuring dependence?
I have read the paper 'Coping with copulas' and it is a bit hard for me to read since it has lots of mathematical equations.
So I am looking for any video lecture on this topic, copula function. I ...
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Verifying two properties of the Clayton Copula
So I'm trying to verify the first two properties of a copula for the Clayton model. The first two properties being:
$C(u_1,…,u_d)$ is non-decreasing in each component, $u_i$
The $i^{th}$ marginal ...
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Bivariate Gaussian copula with exponential margins
I got little bit lost in the formulas.
Assume to have two random variables distributed exponentially $X_i \sim Exp(\lambda_i)$ and $X_j \sim Exp(\lambda_j)$.
Thus, the distribution functions are $...
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Copula- AR simulation
I am estimating different copulas for bond factors that i also fit AR(1) models on.
Now i would like to test and compare durations and VaRs with my model vs empiric.
But how can i simulate AR(1) ...
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Gaussian vs Student Copula applied to finance
I would like to get your opinion on the following topic:
I am comparing the behaviour of Gaussian and Student-t Copulas.
I employ the follwing procedure:
Simulate N=100,000 samples from a Student ...
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How to estimate a copula for time series
I want to estimate a copula for the innovations of two dependent time series (A and B). I have found no reference with a step by step on how to do this. I have only found summarized papers from which ...
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Forecasting conditional returns in DCC-GARCH-copula approach in R
anyone who could help me interpreting and modifying this code?
I have a dataset and want to reserve the last 100 returns for out-of-sample analysis. After specifying and fitting the garch-spd-copula, ...
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Properties of a Symmetric Copula
I am working with the following copula, and have a few questions about it:
$C(x,y) = xy + \theta (1-x)(1-y)xy$
Here $\theta \in [-1,1]$ and $x,y \in [0,1]$
First, I am trying to show this copula is ...
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Joint Distribution of Correlated Variables with Markov Switching
I am modeling a portfolio of correlated assets whose lack of liquidity can be reasonably described by a Markov-switching model. That is, not only is movement size among assets correlated, but so is ...
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Practical Use of Copulas and Sample Generation
I'm currently studying Copulas. However, i did not understand something.
The very basic phases of Copula fitting is as follows i assume;
Model each samples distribution with a parametric(or non-...
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trying to better understand copulas
This topic is dense with notation that makes things a bit confusing. But is this the correct interpretation?
Suppose we have two jointly distributed random variables – $X$ and $Y$ – of arbitrary (but ...
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'GARCH - extreme value theory - copula' approach to estimate risk measures in R
I'm reading about this approach of using GARCH-EVT-copula methodology to separate univariate and joint estimation and then estimate for example VaR and ES. I wanted to try something similar, but my ...
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Marginal Distribution using GARCH model: How to do inverse probability transform?
I have $n$ return series. I fitted AR(1)-GARCH(1,1) to each return series. Then used probability integral transform, PIT(residuals), to transform the residuals to have a uniform distribution. Then I ...
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how to apply a simple copula model
I'm playing around with copulas and wanted to generate some sample based on copula techniques in R. For this purpose I applied the following algorithm:
Generate three sample vectors coming from ...
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Gaussian copula calibration to option price
I have an "exotic" option that is a function of two interest rates (say 3m Libor at 1y maturity and 2y maturity). I assume both the rates follow sabr model (already calibrated to vanillas), ...
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Optimal Hedging Ratio using Copula Models
Let $r_{s, t}$ and $r_{f, t}$ be the return rates of the spot and futures of a commodity at time $t$. The hedging ratio based on variance minimization is calculated by finding the minimum of the ...
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How to combine Gaussian marginals with Gaussian copula to obtain multivariate normals?
in the book "Numerical Methods and Optimization in Finance" I red the following:
"Combining the Gaussian copula with Gaussian marginal gives a fancy way of expressing multivariate normals. However, ...
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Verifying that the extreme value copula is indeed a copula
Given the extreme value copula as defined in Schölzel/Friederichs (2008),
how does one verify that $\frac{\partial C(u_1, u_2)}{\partial u_1} \geq 0?$ For the LHS, I have $$\exp\left[\log(u_1u_2)A\...
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How to sample from a copula in matlab
I have two random variables (say, X and Y). Each of these rv's are defined by their CDFs (CDF_X and CDF_Y). These CDFs were obtained empirically, so they are a "stair" graph.
I also have a copula C ...
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Copulas and default probability
Assume a basket of 3 credits, each with some unconditional default probability ${q_i}(t) = \Pr [{\tau _i} \le t]$.
Consider the joint CDF $H$ of the default times is given by $H(t,t,t) = \Pr [{\tau ...
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Relation of survival and non-survival Marshall-Olkin copula
Let us have two random variables $A$ and $B$ representing lifetimes of two elements of a system, where $A$ has cdf $F_A(x)$, $A \sim Exp(\lambda_1 + \lambda_{12})$ and $B$ has cdf $F_B(y)$, $B \sim ...
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Where does this copula come from?
In a paper I encountered the following notation
$$P(Z\leq z,u\leq Y\leq v)=C(F_{Z}(z),F_{Y}(v)-F_{Y}(u))$$
However I don't see why this holds in relation to uniform random variables. Usually
$$P(Z\...
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Correlation sensitivity in multivariate $t$-copula for portfolio VaR of electricity futures using Kendall's tau-$b$ correlation matrix
My t-copula model captures the daily dollar returns of a portfolio of approximately 400 assets. I am curious if there's a generally accepted way to quantify the sensitivity of portfolio movements with ...
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(Reproducible example) Conditional returns in GARCH-EVT-Copula context (with R)
I'm estimating a time-varying correlation matrix for the normal copula using the rmgarch package from R. I've found this code in the rmgarch.tests folder. I use the ...
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Empirical bivariate copula when one variable is restricted
I am trying to find the empirical copula linking two random variables $X$ and $Y$.
I have some data available but it's limited with respect to the variable $Y$ and I am not convinced it's enough data ...
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What are the general limitations of Gaussian copulas with regards to the range of joint pdf's it can approximate?
I'm working with the nataf transformation - AkA Gaussian copula - and trying to establish the range of joint bivariate pdf's it can approximate, and what limitations it puts on those joint pdf's. I've ...
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Copula Models for Asset Returns
I'm learning about copulas and their applications in finance. When used to assess the dependence structure between two indices for example, can the copula models be estimated directly on the log-...
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Hierarchical copula vs. vine copula
Vine copulas are a sequential cascade of bivariate copulas meant to capture the hierarchical structure in the dependence structure of random variables. How does this relate or differ from the concept ...
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Portofolio optimization using ARMA-GARCH-EVT-Copula
I am currently trying to do some portfolio optimization by reproducing the methodology found in Sahamkhadam, Stephan & Östermark (2018) ("Portfolio optimization based on GARCH-EVT-Copula ...
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Convolution of Dependent Random Variables with Copulas
Lets say I have 2 different observations which are fitted to a parametric distribution.
And lets say that they are dependent and can be modeled by one of the copulas.
I want to calculate “a value” ...