/**
* Euler acceleration to recover a CDF using the Laplace transform of its density
*
* @param f the Laplace transform with complex values of a real valued
* density function
* @param t the point at which the orignal is to be evaluated
* @param h step size used to discretize the integral
* @param N series truncation
* @param M Euler averaging length.
*/
double pnl_ilap_cdf_euler(PnlCmplxFunc *f, double t, double h, int N, int M)
{
int i, Cnp;
double sum, run_sum;
sum = 0.;
for(i=1;i<N+1;i++)
{
sum += sin(i*h*t) * Creal (PNL_EVAL_FUNC(f, Complex (0., h * i))) / (double)i;
}
run_sum = sum; /* partial sum of sn */
sum = 0.0; /* partial exponential sum */
Cnp = 1; /* binomial coefficients */
for(i=0;i<M+1;i++)
{
sum += run_sum * (double) Cnp ;
run_sum += sin ((i + N + 1) * h * t) *
Creal (PNL_EVAL_FUNC(f, Complex (0., h * (i + N + 1)))) / (double) (i + N + 1);
Cnp = (Cnp * (M - i)) / (i + 1);
}
return(2.0 / M_PI * sum / pow(2.0,M) + h * t / M_PI);
}
/**
* Euler acceleration to invert a Laplace transform
*
* @param f the Laplace transform with complex values of a real valued
* function
* @param t the point at which the orignal is to be evaluated
* @param N series truncation
* @param M Euler averaging length.
*/
double pnl_ilap_euler(PnlCmplxFunc *f, double t, int N, int M)
{
int i, Cnp;
double sum, a, pit, run_sum;
double A;
A = 13.; /* MIN (13., 13. / t); */
a = A/(2.0*t);
pit = M_PI/t;
sum = 0.5 * Creal (PNL_EVAL_FUNC(f, Complex (a, 0.)));
for(i=1;i<N+1;i++)
sum += ALTERNATE(i) * Creal (PNL_EVAL_FUNC(f, Complex (a, pit * i)));
run_sum = sum; /* partial sum of sn */
sum = 0.0; /* partial exponential sum */
Cnp = 1; /* binomial coefficients */
for(i=0;i<M+1;i++)
{
sum += run_sum * (double) Cnp ;
run_sum += ALTERNATE(i+N+1) * Creal (PNL_EVAL_FUNC(f, Complex (a, pit * (i + N + 1))));
Cnp = (Cnp * (M - i)) / (i + 1);
}
return exp (A / 2. - M * M_LN2) * sum / t ;
}
/*We use the Cauchy Gourat theorem to compute the derivatives of the double(Mellin+Laplace) transform */
static dcomplex dermellin(dcomplex l, double sg, double r, int nummom)
{
dcomplex term, cv, mu;
int i;
double r0,sumr, sumi/*,x[NPOINTS_FUSAITAGL+1],w[NPOINTS_FUSAITAGL+1]*/;
double v;
double *x,*w;
x=malloc((NPOINTS_FUSAITAGL+1)*sizeof(double));
w=malloc((NPOINTS_FUSAITAGL+1)*sizeof(double));
sumr=0.0;
sumi=0.0;
gauleg(0, 2*M_PI, x, w,NPOINTS_FUSAITAGL);
v = 2*r/(sg*sg)-1.0;
cv = Complex(v,0.0);
mu = Csqrt(Cadd(Complex(v*v,0), RCmul(2.0,l)));
r0 = Creal(RCmul(0.5,Csub(mu,cv)));
if(r0>1.0) r0=0.25;
for (i=1;i<=NPOINTS_FUSAITAGL;i++)
{
term = RCmul(pow(r0,nummom), Cexp(Complex(0.0, nummom*x[i])));
sumr += w[i]*Creal(Cdiv(mellintransform(l, RCmul(r0, Cexp(Complex(0.0, x[i]))), sg, r), term));
sumi += w[i]*Cimag(Cdiv(mellintransform(l, RCmul(r0, Cexp(Complex(0.0, x[i]))), sg, r), term));
}
free(x);
free(w);
return Complex(exp(factln(nummom))*sumr/(2.0*M_PI),exp(factln(nummom))*sumi/(2.0*M_PI));
}
/**
* FFT algorithm to invert a Laplace transform
* @param res a real vector containing the result of the inversion. We know that
* the imaginary part of the inversion vanishes.
* @param f : the Laplace transform to be inverted
* @param T : the time horizon up to which the function is to be recovered
* @param eps : precision required on [0, T]
*/
void pnl_ilap_fft(PnlVect *res, PnlCmplxFunc *f, double T, double eps)
{
PnlVectComplex *fft;
int i, N, size;
double h, time_step, a;
double f_a, omega;
dcomplex mul, fac;
h = M_PI / (2 * T);
a = h * log (1 + 1. / eps) / (M_2PI);
N = MAX (sqrt (exp (a * T) / eps), h / (M_2PI * eps)) ;
N = pow (2., ceil (log (N) / M_LN2) );
time_step = M_2PI / (N * h);
fft = pnl_vect_complex_create (N);
size = floor (T / time_step) + 1;
pnl_vect_resize (res, size);
fac = CIexp (-M_2PI / N);
mul = fac;
f_a = Creal (PNL_EVAL_FUNC (f, Complex (a, 0)));
omega = h;
for (i=0 ; i<N ; i++)
{
pnl_vect_complex_set (fft, i, Cmul(mul,PNL_EVAL_FUNC (f, Complex (a, - omega))));
omega += h;
mul = Cmul(mul,fac);
}
pnl_fft_inplace (fft);
mul = CONE;
for (i=0 ; i<size ; i++)
{
double res_i;
res_i = Creal (Cmul (pnl_vect_complex_get (fft, i), mul));
mul = Cmul (mul, fac);
res_i = (h / M_PI) * exp (a * (i + 1) * time_step) * (res_i + .5 * f_a);
PNL_LET (res, i) = res_i;
}
pnl_vect_complex_free (&fft);
}
double Var_Swap_price(double T,
Levy_diffusion * Model,
dcomplex (*psi)(dcomplex u,double t,Levy_diffusion * model))
{
// phi is hermitian :
// phi(epsilon,0)-phi(-epsilon,0)= 2 Im(phi)(epsilon)
// phi'(0) == Im(phi)(epsilon)/epsilon
// phi(epsilon,0)+phi(-epsilon,0)= 2 Re(phi)(epsilon)
// phi''(0,0)== 2 Re(phi)(epsilon)/epsilon^2
dcomplex Phi = (psi(Complex(EPSILON_DIFF,0.),T,Model));
return 100.0*sqrt(-2.0*Creal(Phi)/(EPSILON_DIFF*EPSILON_DIFF*T));
}
static int pcons (void) {
int ci;
double d;
ci = 0;
switch (Ltok) {
case L_NUMBER:
d = atof (Lstrtok);
ci = (d == (double) (long) d) ? Cinteger ((long) d) : Creal (d);
break;
case L_STRING:
ci = Cstring (Lstrtok);
break;
default:
err ("expected scalar constant, found: %s", Lnames[Ltok]);
}
Lgtok ();
return ci;
}
void newmomentsAM(int model, double rf, double dt, int maxmoment,
int ndates, double parameters[], double **momtable)
{
int i,ii,k;
double sum;
for(i = 1; i < maxmoment + 1; i++)
{momtable[1][i] = Creal(cfrn(model,rf, dt, Complex(0,-i), parameters)); }
for(ii = 2;ii < ndates + 1; ii++)
{for(i = 1; i < maxmoment + 1; i++)
{
sum=0;
for(k=1;k<=i;k++)
{sum=sum+momtable[ii - 1][ k]*bico(i, i-k);
}
momtable[ii][ i] = momtable[1][ i]*(1 + sum);
}
}
}
/**
* Complex Modified Bessel function of the first kind
* divided by exp(|Creal(z)|)
*
* @param z a complex number
* @param v a real number, the order of the Bessel function
*
*/
dcomplex pnl_complex_bessel_i_scaled( double v, dcomplex z )
{
int nz, ierr;
dcomplex cy;
int n = 1;
int kode = 2;
if (v >= 0)
{
pnl_zbesi(CADDR(z), &v, &kode, &n, CADDR(cy), &nz, &ierr);
DO_MTHERR("ive:");
}
else
{
dcomplex aux1, aux2;
aux1 = pnl_complex_bessel_i_scaled (-v, z);
aux2 = pnl_complex_bessel_k (-v, z);
aux2 = CRmul (aux2, M_2_PI * sin(M_PI * -v) * exp ( -fabs ( Creal(z) ) ));
cy = Cadd (aux1, aux2);
}
return cy;
}
double Var_Swap_price_Levy(Levy_process * Model,
dcomplex (*psi)(dcomplex u,Levy_process * model))
{
/*
dcomplex Phip = (psi(Complex(EPSILON_DIFF,0.),Model));
dcomplex Phi0 = (psi(Complex(0.,0.),Model));
dcomplex Phim = (psi(Complex(-EPSILON_DIFF,0.),Model));
dcomplex dPhi=Csub(Phip,Phim);
Phi0=Csub(Cadd(Phip,Phim),RCmul(2.,Phi0));
return 100.0*sqrt((Creal(Phi0)+0.25*Creal(dPhi)*Creal(dPhi))/(EPSILON_DIFF*EPSILON_DIFF));
*/
// psi is hermitian :
// psi(epsilon,0)-psi(-epsilon,0)= 2 Im(psi)(epsilon)
// psi'(0) == Im(psi)(epsilon)/epsilon
// psi(epsilon,0)+psi(-epsilon,0)= 2 Re(psi)(epsilon)
// psi''(0,0)== 2 Re(psi)(epsilon)/epsilon^2
dcomplex Phi = (psi(Complex(EPSILON_DIFF,0.),Model));
return 100.0*sqrt(2.0*Creal(Phi)/(EPSILON_DIFF*EPSILON_DIFF));
}
//swaption_payer_receiver=0 : Payer
//swaption_payer_receiver=1 : Receiver
static double cf_swaption_direct(StructLiborAffine *LiborAffine, double swaption_start, double swaption_end, double swaption_period, double swaption_strike, double swaption_nominal, int swaption_payer_receiver)
{
double x0, lambda, theta, eta, Sqr_eta, Y;
double P=0., Q=0., x, deg_freedom, n_centrality_param, bound, price, trm_k;
double Tk, a_Ti, b_Ti, dzeta_k, sigma_k, sum=0.;
int i, m, k, which=1, status;
double psi_d;
dcomplex uk, phi, psi;
x0 = GET(LiborAffine->ModelParams, 0);
lambda = GET(LiborAffine->ModelParams, 1);
theta = GET(LiborAffine->ModelParams, 2);
eta = GET(LiborAffine->ModelParams, 3);
Sqr_eta = SQR(eta);
// Static variables
Ti = swaption_start;
Tm = swaption_end;
TN = LET(LiborAffine->TimeDates, (LiborAffine->TimeDates)->size-1);
i = indiceTimeLiborAffine(LiborAffine, Ti);
m = indiceTimeLiborAffine(LiborAffine, Tm);
c_k = pnl_vect_create_from_double(m-i+1, swaption_period*swaption_strike);
Phi_i_k = pnl_vect_create(m-i+1);
Psi_i_k = pnl_vect_create(m-i+1);
LET(c_k, 0) = -1.0;
LET(c_k, m-i) += 1.;
for (k=i; k<=m; k++)
{
uk = Complex(GET(LiborAffine->MartingaleParams, k), 0.);
phi_psi_t_v(TN-Ti, uk, LiborAffine, &phi, &psi);
LET(Phi_i_k, k-i) = Creal(phi);
LET(Psi_i_k, k-i) = Creal(psi);
}
// Zero of the function f
if (m==i+1) Y = find_Y_caplet(LiborAffine);
else Y = find_Y_swaption(LiborAffine);
a_Ti = exp(-lambda*Ti);
if (lambda == 0.) b_Ti = Ti;
else b_Ti = (1.-a_Ti)/lambda;
deg_freedom = lambda*theta/Sqr_eta;
sum=0.;
Tk=Ti;
for (k=i; k<=m; k++)
{
psi_d = GET(Psi_i_k, k-i);
dzeta_k = 1 - 2*Sqr_eta*b_Ti*psi_d;
sigma_k = Sqr_eta*b_Ti/dzeta_k;
x = Y/sigma_k;
n_centrality_param = x0*a_Ti/(Sqr_eta*b_Ti*dzeta_k);
if (x<0)
{
P=0.;
Q=1.;
}
else
{
pnl_cdf_chn (&which, &P, &Q, &x, °_freedom, &n_centrality_param, &status, &bound);
}
if (swaption_payer_receiver==0)
trm_k = -GET(c_k, k-i)*BondPrice(Tk, LiborAffine->ZCMarket) * Q;
else
trm_k = GET(c_k, k-i)*BondPrice(Tk, LiborAffine->ZCMarket) * P;
sum += trm_k;
Tk += swaption_period;
}
price = swaption_nominal * sum;
pnl_vect_free(&c_k);
pnl_vect_free(&Phi_i_k);
pnl_vect_free(&Psi_i_k);
return price;
}
