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diff --git a/R/tranche_functions.R b/R/tranche_functions.R new file mode 100644 index 00000000..0bccdf02 --- /dev/null +++ b/R/tranche_functions.R @@ -0,0 +1,531 @@ +library(lossdistrib) +pos <- function(x){ + pmax(x, 0) +} + +trancheloss <- function(L, K1, K2){ + pos(L - K1) - pos(L - K2) +} + +trancherecov <- function(R, K1, K2){ + pos(R - 1 + K2) - pos(R - 1 +K1) +} + +tranche.cl <- function(L, R, cs, K1, K2, Ngrid=nrow(L), scaled=FALSE){ + ## computes the couponleg of a tranche + ## if scaled is TRUE, scale it by the size of the tranche (K2-K1) + ## can make use of the fact that the loss and recov distribution are + ## truncated (in that case nrow(L) != Ngrid + if(K1==K2){ + return( 0 ) + }else{ + support <- seq(0, 1, length=Ngrid)[1:nrow(L)] + size <- K2 - K1 - crossprod(trancheloss(support, K1, K2), L) - + crossprod(trancherecov(support, K1, K2), R) + sizeadj <- as.numeric(0.5 * (size + c(K2-K1, size[-length(size)]))) + if(scaled){ + return( 1/(K2-K1) * crossprod(sizeadj * cs$coupons, cs$df) ) + }else{ + return( crossprod(sizeadj * cs$coupons, cs$df) ) + } + } +} + +tranche.cl.scenarios <- function(l, r, cs, K1, K2, scaled=FALSE){ + ## computes the couponleg of a tranche for one scenario + ## if scaled is TRUE, scale it by the size of the tranche (K2-K1) + ## can make use of the fact that the loss and recov distribution are + ## truncated (in that case nrow(L) != Ngrid + if(K1==K2){ + return( 0 ) + }else{ + size <- K2 - K1 - trancheloss(l, K1, K2) - trancherecov(r, K1, K2) + sizeadj <- as.numeric(0.5 * (size + c(K2-K1, size[-length(size)]))) + if(scaled){ + return( 1/(K2-K1) * crossprod(sizeadj * cs$coupons, cs$df) ) + }else{ + return( crossprod(sizeadj * cs$coupons, cs$df) ) + } + } +} + +funded.tranche.pv <- function(L, R, cs, K1, K2, scaled = FALSE){ + if(K1==K2){ + return(0) + }else{ + size <- K2 - K1 -trancheloss(L, K1, K2) - trancherecov(R, K1, K2) + sizeadj <- as.numeric(0.5 * (size + c(K2-K1, size[-length(size)]))) + interest <- crossprod(sizeadj * cs$coupons, cs$df) + principal <- diff(c(0, trancherecov(R, K1, K2))) + principal[length(principal)] <- principal[length(principal)] + size[length(size)] + principal <- crossprod(cs$df, principal) + if(scaled){ + pv <- (interest + principal)/(K2-K1) + }else{ + pv <- (interest + principal) + } + return(pv) + } +} + +tranche.pl <- function(L, cs, K1, K2, Ngrid=nrow(L), scaled=FALSE){ + ## computes the protection leg of a tranche + ## if scaled + if(K1==K2){ + return(0) + }else{ + support <- seq(0, 1, length=Ngrid)[1:nrow(L)] + cf <- K2 - K1 - crossprod(trancheloss(support, K1, K2), L) + cf <- c(K2 - K1, cf) + if(scaled){ + return( 1/(K2-K1) * crossprod(diff(cf), cs$df)) + }else{ + return( crossprod(diff(cf), cs$df)) + } + } +} + +tranche.pl.scenarios <- function(l, cs, K1, K2, scaled=FALSE){ + ## computes the protection leg of a tranche + ## if scaled + if(K1==K2){ + return(0) + }else{ + cf <- K2 - K1 - trancheloss(l, K1, K2) + cf <- c(K2 - K1, cf) + if(scaled){ + return( 1/(K2-K1) * as.numeric(crossprod(diff(cf), cs$df))) + }else{ + return( as.numeric(crossprod(diff(cf), cs$df))) + } + } +} + +tranche.pv <- function(L, R, cs, K1, K2, Ngrid=nrow(L)){ + return( tranche.pl(L, cs, K1, K2, Ngrid) + tranche.cl(L, R, cs, K1, K2, Ngrid)) +} + +tranche.pv.scenarios <- function(l, r, cs, K1, K2){ + return( tranche.pl.scenarios(l, cs, K1, K2, TRUE) + + tranche.cl.scenarios(l, r, cs, K1, K2, TRUE)) +} + +adjust.attachments <- function(K, losstodate, factor){ + ## computes the attachments adjusted for losses + ## on current notional + return( pmin(pmax((K-losstodate)/factor, 0),1) ) +} + +BCtranche.legs <- function(index, K, rho, complement=FALSE){ + ## computes the protection leg and couponleg of a 0-K tranche + ## if complement==TRUE, computes the protection leg and coupon leg of a K-1 tranche + if((K==0 && !complement) || (K==1 && complement)){ + return(list(cl=0, pl=0)) + }else if((K==1 && !complement) || (K==0 && complement)){ + return(BCindex.pv(index)) + }else{ + dist <- BClossdistC(index$defaultprob, index$issuerweights, index$recov, rho, index$Z, index$w, index$N) + if(complement){ + return(list(cl=tranche.cl(dist$L, dist$R, index$cs, K, 1), + pl=tranche.pl(dist$L, index$cs, K, 1))) + }else{ + return(list(cl=tranche.cl(dist$L, dist$R, index$cs, 0, K), + pl=tranche.pl(dist$L, index$cs, 0, K))) + } + } +} + +BCtranche.pv <- function(index, protection=FALSE, complement=FALSE){ + ## computes the protection leg, couponleg, and bond price of a tranche + ## in the base correlation setting + ## if complement=FALSE compute the pvs starting from 0 (bottom-up skew) + ## if complement=TRUE compute the pvs starting from 1 (top-down skew) + pl <- rep(0, length(index$rho)) + cl <- rep(0, length(index$rho)) + for(i in seq_along(index$rho)){ + temp <- BCtranche.legs(index, index$K[i], index$rho[i], complement) + pl[i] <- temp$pl + cl[i] <- temp$cl + } + dK <- diff(index$K) + plvec <- diff(pl)/dK + clvec <- diff(cl)/dK*index$tranches$running + if(complement){ + plvec <- -plvec + clvec <- -clvec + } + if(protection){ + bp <- -plvec-clvec + }else{ + bp <- 1+plvec+clvec + } + return(list(pl=plvec, cl=clvec, bp=bp)) +} + +MFtranche.pv <- function(index, dist, protection=FALSE){ + n.tranches <- length(index$K)-1 + pl <- rep(0, n.tranches) + cl <- rep(0, n.tranches) + for(i in seq.int(n.tranches)){ + pl[i] <- tranche.pl(dist$L, index$cs, index$K[i], index$K[i+1]) + cl[i] <- tranche.cl(dist$L, dist$R, index$cs, index$K[i], index$K[i+1]) + } + dK <- diff(index$K) + plvec <- pl/dK + clvec <- cl/dK*index$tranches$running + if(protection){ + bp <- -plvec-clvec + }else{ + bp <- 1+plvec+clvec + } + return(list(pl=plvec, cl=clvec, bp=bp)) +} + +adjust.skew <- function(index1, index2, method="ATM"){ + #index1 is the index for which we already have computed the skew + #index2 is the index we're mapping to + # if method="ATM", do simple at the money mapping + # method="TLP", do tranche loss proportion mapping + # method="PM", do probability matching + + K1 <- index1$K[-c(1,length(index1$K))] + K2 <- index2$K[-c(1,length(index2$K))] + aux <- function(x, index1, el1, skew, index2, el2, K2){ + return(abs(ELtrunc(index1, x, skew(x))/el1- + ELtrunc(index2, K2, skew(x))/el2)) + } + aux2 <- function(x, index1, skew, index2, K2){ + return(abs(log(Probtrunc(index1, x, skew(x)))- + log(Probtrunc(index2, K2, skew(x))))) + } + if(method %in% c("ATM", "TLP")){ + el1 <- EL(index1) + el2 <- EL(index2) + } + skew <- function(x){ + #we cap the correlation at 0.99 and 0.01 + f <- splinefun(K1, index1$rho[-c(1, length(index1$rho))], "natural") + return(pmax(pmin(f(x), 0.99), 0.01)) + } + if(method=="ATM"){ + K1eq <- el1/el2 * K2 + }else if(method == "TLP"){ + K1eq <- c() + m <- max(K2) + 0.3 + for(K2val in K2){ + prog <- optimize(aux, interval=c(0,m), + index1=index1, el1=el1, skew=skew, + index2=index2, el2=el2, K2=K2val) + K1eq <- c(K1eq, prog$minimum) + } + }else if (method=="PM"){ + K1eq <- c() + m <- max(K2) + 0.25 + for(K2val in K2){ + prog <- optimize(aux2, interval=c(0, m), + index1=index1, skew=skew, index2=index2, K2=K2val) + K1eq <- c(K1eq, prog$minimum) + } + } + return(c(NA, skew(K1eq), NA)) +} + +theta.adjust.skew <- function(index, shortened=4, method="ATM"){ + #ajust the correlation skew by doing ATM mapping on the expected loss + indexshort <- index + N <- nrow(index$cs)-shortened + indexshort$defaultprob <- indexshort$defaultprob[,1:N] + indexshort$cs <- indexshort$cs[1:N,] + return(adjust.skew(index, indexshort, method)) +} + +BCtranche.theta <- function(index, shortened=4, complement=FALSE, method="ATM"){ + temp <- BCtranche.pv(index, complement=complement) + rho.adj <- theta.adjust.skew(index, shortened, method) + if(any(rho.adj[-c(1, length(rho.adj))]<=0)){ + print("probable inverted skew: no adjustment") + }else{ + index$rho <- rho.adj + } + N <- nrow(index$cs) - shortened + index$cs <- index$cs[1:N,] + index$defaultprob <- index$defaultprob[,1:N] + temp2 <- BCtranche.pv(index, complement=complement) + temp3 <- BCtranche.delta(index, complement=complement) + return(data.frame(theta=temp2$bp-temp$bp+index$tranches$running, + fw.delta=temp3$delta)) +} + +BCtranche.delta <- function(index, complement=FALSE){ + ## computes the tranche delta (on current notional) by doing a proportional + ## blip of all the curves + ## if complement is False, then computes deltas bottom-up + ## if complement is True, then computes deltas top-down + eps <- 1e-4 + index$N <- 301 ## for gamma computations we need all the precision we can get + ## we build a lit of 4 indices with various shocks + index.list <- lapply(c(0, eps, -eps, 2*eps), function(x){ + if(x==0){ + return(index) + }else{ + newindex <- index + newindex$portfolio <- tweakportfolio(newindex$portfolio, x) + newindex$defaultprob <- 1 - SPmatrix(newindex$portfolio, length(index$cs$dates)) + return(newindex) + } + }) + bp <- matrix(0, length(index$K)-1, length(index.list)) + indexbp <- rep(0, length(index.list)) + for(j in seq_along(index.list)){ + indexbp[j] <- BCindex.pv(index.list[[j]])$bp + bp[,j] <- BCtranche.pv(index.list[[j]], complement=complement)$bp + } + + deltas <- (bp[,2]-bp[,3])/(indexbp[2]-indexbp[3])*tranche.factor(index)/index$factor + deltasplus <- (bp[,4]-bp[,1])/(indexbp[4]-indexbp[1])*tranche.factor(index)/index$factor + gammas <- (deltasplus-deltas)/(indexbp[2]-indexbp[1])/100 + + return( data.frame(delta=deltas, gamma=gammas) ) +} + +MFtranche.delta <- function(index){ + ## computes the tranche delta (on current notional) by doing a proportional + ## blip of all the curves + ## if complement is False, then computes deltas bottom-up + ## if complement is True, then computes deltas top-down + eps <- 1e-4 + index$Ngrid <- 301 ## for gamma computations we need all the precision we can get + ## we build a lit of 4 indices with various shocks + index.list <- lapply(c(0, eps, -eps, 2*eps), function(x){ + if(x==0){ + return(index) + }else{ + newindex <- index + newindex$portfolio <- tweakportfolio(newindex$portfolio, x) + newindex$defaultprob <- 1 - SPmatrix(newindex$portfolio, length(index$cs$dates)) + return(newindex) + } + }) + bp <- matrix(0, length(index$K)-1, length(index.list)) + indexbp <- rep(0, length(index.list)) + for(j in seq_along(index.list)){ + indexbp[j] <- BCindex.pv(index.list[[j]])$bp + dist <- MFdist(index.list[[j]]) + bp[,j] <- BCtranche.pv(index.list[[j]], dist) + } + + deltas <- (bp[,2]-bp[,3])/(indexbp[2]-indexbp[3])*tranche.factor(index)/index$factor + deltasplus <- (bp[,4]-bp[,1])/(indexbp[4]-indexbp[1])*tranche.factor(index)/index$factor + gammas <- (deltasplus-deltas)/(indexbp[2]-indexbp[1])/100 + + return( list(deltas=deltas, gammas=gammas) ) +} + +BCtranche.corr01 <- function(index, eps=0.01, complement=FALSE){ + ##does a parallel shift of the skew and computes the change in pv + before <- BCtranche.pv(index, complement=complement) + index$rho[-1] <- index$rho[-1]+eps + after <- BCtranche.pv(index, complement=complement) + return(after$bp-before$bp) +} + +EL <- function(index, discounted=TRUE, shortened=0){ + ## computes the expected loss of a portfolio (time discounted if discounted is TRUE) + ## given the default curves and recovery + ## should be very close to the protection leg of the portfolio of cds + ## index should be a list with issuerweights, recov, defaultprob and cs parameters + ## shortened: number of quarters to shorten the maturity by + Ncol <- ncol(index$defaultprob)-shortened + ELvec <- as.numeric(crossprod(index$issuerweights * (1-index$recov), index$defaultprob[,1:Ncol])) + if(!discounted){ + return( ELvec[length(ELvec)] ) + }else{ + return( sum(index$cs$df[1:Ncol]*diff(c(0, ELvec))) ) + } +} + +BCindex.pv <- function(index, discounted=TRUE, shortened=0){ + Ncol <- ncol(index$defaultprob)-shortened + ELvec <- as.numeric(crossprod(index$issuerweights * (1-index$recov), index$defaultprob[,1:Ncol])) + size <- 1-as.numeric(crossprod(index$issuerweights, index$defaultprob[,1:Ncol])) + sizeadj <- 0.5*(c(1, size[-length(size)])+size) + if(!discounted){ + pl <- -ELvec[length(ELvec)] + cl <- as.numeric(crossprod(index$cs$coupons[1:Ncol], sizeadj)) + bp <- 1+cl+pl + }else{ + pl <- -sum(index$cs$df[1:Ncol]* diff(c(0, ELvec))) + cl <- as.numeric(crossprod(index$cs$coupons[1:Ncol], sizeadj * index$cs$df[1:Ncol] )) + bp <- 1+cl+pl + } + bp <- 1+cl*index$quotes$spread+pl + return(list(pl=pl, cl=cl, bp=bp)) +} + +ELtrunc <- function(index, K, rho){ + ## computes the expected loss of a portfolio below strike K + ## could be written faster by using a truncated version of lossdist + ## index should be a list with issuerweights, recov, defaultprob and cs parameters + dist <- BClossdistC(index$defaultprob, index$issuerweights, index$recov, rho, index$Z, index$w, index$N) + return( -tranche.pl(dist$L, index$cs, 0, K)) +} + +Probtrunc <- function(index, K, rho){ + dist <- BClossdistC(index$defaultprob, index$issuerweights, index$recov, rho, index$Z, index$w, index$N) + p <- cumsum(dist$L[,ncol(dist$L)]) + support <- seq(0, 1, length=index$N) + probfun <- splinefun(support, p, method="hyman") + return(probfun(K)) +} + + +BCstrikes <- function(index, K, rho) { + ## computes the strikes as a percentage of expected loss + ## Kmodified is the current attachment points (adjusted for losses) + el <- EL(index) + ELvec <- c() + for(i in 2:length(K)){ + ELvec <- c(ELvec, ELtrunc(index, K[i], rho[i])) + } + return( ELvec/el ) +} + +tranche.factor <- function(index){ + ## compute the factor to convert from delta on current notional to delta on original notional + ## K1 and K2 original strikes + return( diff(index$K)/diff(index$K.orig)*index$factor ) +} + +MFupdate.prob <- function(Z, w, rho, defaultprob, useC = TRUE){ + ## update the probabilites based on a non gaussian factor + ## distribution so that the pv of the cds stays the same. + p <- matrix(0, nrow(defaultprob), ncol(defaultprob)) + fit.prob <- if(useC) fit.probC else fit.prob + for(i in 1:nrow(defaultprob)){ + for(j in 1:ncol(defaultprob)){ + p[i,j] <- fit.prob(Z, w, rho[i], defaultprob[i,j]) + } + } + return( p ) +} + +MFlossrecovdist.prepay <- function(w, Z, rho, defaultprob, defaultprobmod, prepayprob, prepayprobmod, + issuerweights, recov, Ngrid=2*length(issuerweights)+1, defaultflag=FALSE){ + ## computes the loss and recovery distribution using the modified factor distribution + n.credit <- length(issuerweights) + n.int <- length(w) + Rstoch <- array(0, dim=c(n.int, n.credit, ncol(defaultprob))) + for(t in 1:ncol(defaultprob)){ + for(i in 1:n.credit){ + Rstoch[,i,t] <- stochasticrecov(recov[i], 0, Z, w, rho, defaultprob[i,t], defaultprobmod[i,t]) + } + } + parf <- function(i){ + dpshocked <- apply(defaultprobmod, 2, shockprob, rho=rho, Z=Z[i]) + ppshocked <- apply(prepayprobmod, 2, shockprob, rho=rho, Z=-Z[i]) + S <- 1 - Rstoch[i,,] + dist <- lossrecovdist.term(dpshocked, ppshocked, issuerweights, S, Ngrid, defaultflag) + } + L <- matrix(0, Ngrid, ncol(defaultprob)) + R <- matrix(0, Ngrid, ncol(defaultprob)) + for(i in 1:length(w)){ + dist <- parf(i) + L <- L + dist$L * w[i] + R <- R + dist$R * w[i] + } + return( list(L=L, R=R) ) +} + +MFlossdist.joint <- function(cl, w, Z, rho, defaultprob, defaultprobmod, issuerweights, recov, + Ngrid=2*length(issuerweights)+1, defaultflag=FALSE){ + ## rowSums(Q) is the default/loss distribution depending if + ## defaultflag is TRUE or FALSE (default setting is FALSE) + ## colSums(Q) is the recovery distribution + ## so that recovery is the y axis and L/D is the x axis + ## if we use the persp function, losses is the axis facing us, + ## and R is the axis going away from us. + n.credit <- length(issuerweights) + n.int <- lenth(w) + Rstoch <- array(0, dim=c(n.int, n.credit, ncol(defaultprob))) + for(t in 1:ncol(defaultprob)){ + for(i in 1:n.credit){ + Rstoch[,i,t] <- stochasticrecov(recov[i], 0, Z, w, rho, defaultprob[i,t], defaultprobmod[i,t]) + } + } + parf <- function(i){ + pshocked <- apply(defaultprobmod, 2, shockprob, rho=rho, Z=Z[i]) + S <- 1 - Rstoch[i,,] + dist <- lossrecovdist.joint.term(pshocked, 0, issuerweights, S, Ngrid, defaultflag) + gc() + return(dist) + } + temp <- parSapply(cl, 1:length(w), parf) + clusterCall(cl, gc) + Q <- array(0, dim=c(ncol(defaultprob), Ngrid, Ngrid)) + for(i in 1:length(w)){ + Q <- Q + w[i]*array(temp[,i], dim=c(ncol(defaultprob), Ngrid, Ngrid)) + } + return( Q ) +} + +MFlossdist.prepay.joint <- function(w, Z, rho, defaultprob, defaultprobmod, + prepayprob, prepayprobmod, issuerweights, recov, + Ngrid=2*length(issuerweights)+1, defaultflag=FALSE){ + ## rowSums is the loss distribution + ## colSums is the recovery distribution + ## so that recovery is the y axis and L is the x axis + ## if we use the persp function, losses is the axis facing us, + ## and R is the axis going away from us. + n.credit <- length(issuerweights) + n.int <- length(w) + Rstoch <- array(0, dim=c(n.credit, n.int, ncol(defaultprob))) + + for(t in 1:ncol(defaultprob)){ + for(i in 1:n.credit){ + Rstoch[i,,t] <- stochasticrecovC(recov[i], 0, Z, w, rho[i], + defaultprob[i,t], defaultprobmod[i,t]) + } + } + Q <- array(0, dim=c(ncol(defaultprob), Ngrid, Ngrid)) + for(t in 1:ncol(defaultprob)){ + S <- 1 - Rstoch[,,t] + Q[t,,] <- lossdistC.prepay.jointZ(defaultprobmod[,t], prepayprobmod[,t], + issuerweights, S, Ngrid, defaultflag, rho, Z, w) + } + return( Q ) +} + +MFrecovery <- function(index, defaultprobmod){ + n.credit <- length(index$issuerweights) + n.int <- length(index$Z) + Rstoch <- array(0, dim=c(n.credit, n.int, ncol(index$defaultprob))) + rho <- rep(0.45, n.credit) + for(t in 1:ncol(index$defaultprob)){ + for(i in 1:n.credit){ + Rstoch[i,,t] <- stochasticrecovC(index$recov[i], 0, index$Z, index$w.mod, + rho[i], index$defaultprob[i,t], defaultprobmod[i,t]) + } + } + return( Rstoch ) +} + +MFlossdist <- function(index){ + n.credit <- length(index$issuerweights) + rho <- rep(0.45, n.credit) + defaultprobmod <- MFupdate.probC(index$Z, index$w.mod, rho, index$defaultprob) + n.credit <- length(index$issuerweights) + n.int <- length(index$Z) + Rstoch <- MFrecovery(index, defaultprobmod) + Lw <- matrix(0, index$N, n.int) + Rw <- matrix(0, index$N, n.int) + L <- matrix(0, index$N, ncol(index$defaultprob)) + R <- matrix(0, index$N, ncol(index$defaultprob)) + for(t in 1:ncol(index$defaultprob)){ + S <- 1 - Rstoch[,,t] + Lw <- lossdistCZ(defaultprobmod[,t], index$issuerweights, S, index$N, 0, rho, index$Z) + Rw <- lossdistCZ(defaultprobmod[,t], index$issuerweights, 1-S, Ngrid, 0, rho, index$Z) + L[,t] <- Lw%*%index$w.mod + R[,t] <- Rw%*%index$w.mod + } + return(list(L=L, R=R)) +} |
