xuruilong100 发表于 2012-7-30 10:10
sptprice = zeros(100,1);
optprice = zeros(100,1);
for(i = 1:100)
我试着把6张图的上届都定为300,发现这回显式看涨和显式看跌的图像都出不来,但隐式看涨、隐式看跌、CN看涨、CN看跌的图像都出来了,而且这4张图中,看跌的2张图和上届定为100的几乎没区别,看涨的2张图的option price的最高点由原先的不到50变成了超过50.
为什么这次显式的会出问题呢?
是不是我不需要把所有的上届都改为300,只需把隐式改为300,显式和CN仍然定为100呢?
显式的程序 如下
function oPrice = finDiffExplicit(X,S0,r,sig,Svec,tvec,oType)
% Function to calculate the price of a vanilla European
% Put or Call option using the explicit finite difference method
%
% oPrice = finDiffExplicit(X,r,sig,Svec,tvec,oType)
%
% Inputs: X - strike
% : S0 - stock price
% : r - risk free interest rate
% : sig - volatility
% : Svec - Vector of stock prices (i.e. grid points)
% : tvec - Vector of times (i.e. grid points)
% : oType - must be 'PUT' or 'CALL'.
%
% Output: oPrice - the option price
%
% Notes: This code focuses on details of the implementation of the
% explicit finite difference scheme.
% It does not contain any programatic essentials such as error
% checking.
% It does not allow for optional/default input arguments.
% It is not optimized for memory efficiency, speed or
% use of sparse matrces.
% Author: Phil Goddard (
phil@goddardconsulting.ca)
% Date : Q4, 2007
% Get the number of grid points
M = length(Svec)-1;
N = length(tvec)-1;
% Get the grid sizes (assuming equi-spaced points)
dt = tvec(2)-tvec(1);
% Calculate the coefficients
% To do this we need a vector of j points
j = 1:M-1;
sig2 = sig*sig;
j2 = j.*j;
aj = 0.5*dt*(sig2*j2-r*j);
bj = 1-dt*(sig2*j2+r);
cj = 0.5*dt*(sig2*j2+r*j);
% Pre-allocate the output
price(1:M+1,1:N+1) = nan;
% Specify the boundary conditions
switch oType
case 'CALL'
% Specify the expiry time boundary condition
price(:,end) = max(Svec-X,0);
% Put in the minimum and maximum price boundary conditions
% assuming that the largest value in the Svec is
% chosen so that the following is true for all time
price(1,:) = 0;
price(end,:) = (Svec(end)-X)*exp(-r*tvec(end:-1:1));
case 'PUT'
% Specify the expiry time boundary condition
price(:,end) = max(X-Svec,0);
% Put in the minimum and maximum price boundary conditions
% assuming that the largest value in the Svec is
% chosen so that the following is true for all time
price(1,:) = (X-Svec(end))*exp(-r*tvec(end:-1:1));
price(end,:) = 0;
end
% Form the tridiagonal matrix
A = diag(bj); % Diagonal terms
A(2:M:end) = aj(2:end); % terms below the diagonal
A(M:M:end) = cj(1:end-1); % terms above the diagonal
% Calculate the price at all interior nodes
offsetConstants = [aj(1); cj(end)];
for i = N:-1:1
price(2:end-1,i) = A*price(2:end-1,i+1);
% Offset the first and last terms
price([2 end-1],i) = price([2 end-1],i) + ...
offsetConstants.*price([1 end],i+1);
end
% Calculate the option price
oPrice = interp1(Svec,price(:,1),S0);
画图程序 如下
>> sptprice = zeros(100,1);
optprice = zeros(100,1);
for(i = 1:100)
sptprice(i,1) = i;
optprice(i,1) = finDiffExplicit(50,sptprice(i,1),0.05,0.3,0:1:300,0:0.001:1,'CALL');
end
plot(sptprice,optprice,'-')
grid on
>> sptprice = zeros(100,1);
optprice = zeros(100,1);
for(i = 1:100)
sptprice(i,1) = i;
optprice(i,1) = finDiffExplicit(50,sptprice(i,1),0.05,0.3,0:1:300,0:0.001:1,'PUT');
end
plot(sptprice,optprice,'-')
grid on