octave runs ok but plot is not displayed?

Question

HI there I am using Octave 2.3.4 with a plot command. I am new at Octave. This plot does not display for some reason. Here is my M file sample:

        1;

clear all;

%%%%%%%%% parameters setting  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
r=0.01; %risk free rate
S0=50; %underlying price 1

%create an implied volatiltiy surface using below parameters:
basevol=0.25; %implied volatility at time t=0 and in center of strike axis
skewT=-0.001; %icrease in vol for one unit increase in maturity
v1=0.1; %defines how much a smile is raised at left end from base vol
v3=0.2; %defines how much a smile is raised at right end from base vol

nK=100; %no. of strike steps
nT=10; %no. of time steps
Tmax=1; %maximum value in time axis
Kmin=1; %minimum value in strike price axis 
Kmax=150; %maximum value of strike price axis
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 


dt=Tmax/(nT-1);
Tvec=0:dt:1;
dk=(Kmax-Kmin)/(nK-1);
Kvec=Kmin:dk:Kmax;
Tvec=Tvec';
Kvec=Kvec';
nK=size(Kvec,1);
nT=size(Tvec,1);
dvolT=ones(nK,nT)*(skewT*dt);
dvolT=cumsum(dvolT,2);

SmileVec=GetSmile(Kvec,v1,0,v3);
dvolK=ones(nK,nT);
dvolK=repmat(SmileVec,1,nT);

ImpliedVolSurface=ones(nK,nT)*basevol+dvolT+dvolK;

%use formula mentioned by John Elder in "Hedging for Financial Derivatives"
%this formula gives local volatility using implied volatility 
function ret=GetLocalVolSurface(ImpliedVolSurface, S, r, Kvec, Tvec)
  [m,n]=size(ImpliedVolSurface);
  LocalVolSurface=zeros(m,n);
  dk=Kvec(2)-Kvec(1);
  dt=Tvec(2)-Tvec(1);
  x=ImpliedVolSurface;
  for i=3:m-2, %loop over strikes
    for j=1:n-1, %loop over time steps
      dv_dk=(x(i+1,j)-x(i-1,j))/(2*dk);
      dv2_dk2=(x(i-1,j)-2*x(i,j)+x(i+1,j))/(dk*dk);
      dv_dt=(x(i,j+1)-x(i,j))/dt;
      K=Kvec(i);
      T=Tvec(j+1);
      rT=T^0.5;
      sig=x(i,j);
      h1=(log(S/K)+r*T+0.5*sig*sig*T)/(sig*rT);
      numer=sig*sig + 2*T*sig*dv_dt + 2*r*K*T*sig*dv_dk;
      denom=(1+K*h1*rT*dv_dk)^2 + K*K*T*sig*sig*(dv2_dk2-h1*dv_dk*dv_dk*rT);
      LocalVolSurface(i,j)=(numer/denom)^0.5;
    end
  end
  ret=LocalVolSurface;
endfunction


LocalVol_Surface=GetLocalVolSurface(ImpliedVolSurface,S0,r,Kvec,Tvec);

AsyImplVols=zeros(nK,1);
T=Tvec(nT-1);
F=S0*exp(r*T);

for i=3:nK-2,
    % use formula sigBS(F,K)=sigLoc( (F+K)/2 )
    K=Kvec(i);
    lookupK=(F+K)/2;
    kdiff=abs(Kvec-lookupK); %try to find nearest point in grid
    kidx=min(find(kdiff==min(kdiff)));
    if ( (kidx > 3) && (kidx < nK-2) ),
        AsyImplVols(i)=LocalVol_Surface(kidx);
    else
        AsyImplVols(i) = NaN;
    end
end
figure(1);
plot(Kvec(3:nK-2),[ImpliedVolSurface(3:nK-2,nT-1) LocalVol_Surface(3:nK-2,nT-1) AsyImplVols(3:nK-2)]);

When I run in Octave with no error, the plot is never displayed. It does include gnuplot 1.0.1 which I understand does the graph? Is there something I am not doing or missing? I am also running this on Windows 2003 Server. Thanks

Answer 1

I got the answer here. Octave by default uses fltk for plotting etc, which is failing to work, using gnuplot works here. Just add below lines to .octaverc file in your home directory.

graphics_toolkit("gnuplot")

So that every time octave starts it will set the default package for plotting to gnuplot

Answer 2

I do know that's an old question but since I ran into quite the same error yesterday, maybe this can help someone else, too:

According to the Octave wiki pages, there seems to be a problem with plotting and the "oct2mat"-library. For me, the problem was solved after I ran this at the octave command prompt:

pkg rebuild -noauto oct2mat

and restarted octave. When you need to use "oct2mat", type:

pkg load oct2mat

Hope that helps!