function pvmean( iter )
clear
clear path 

global Nx Ny Nz
global lat long dz dm mdep
global delt_su su_its t_su delt
global descriptor this_path
global f deltaf Q beta r_expt r_heat H
global time rots it
global g Cp rho_bar alpha
global u v t w
global iterations


param_file_name =   ...
   input(' Please enter the name of the m-file with the parameters for this run : ','s') ;
feval(param_file_name) ;

iterations

itstart = input(' Please enter start iteration : ','s') 
itend = input(' Please enter end iteration : ','s') 


sizeit=size(iterations);
for i=1:sizeit(1)
iter(i)=eval(iterations(i,1:10));
end
nitstart=find(iter==eval(itstart))
nitend=find(iter==eval(itend))

path   = this_path 
cmdstr=['cd ' path ];
eval(cmdstr);
path=pwd

sumtheta=zeros(Nx,Ny,Nz);
sumu=zeros(Nx,Ny,Nz);
sumv=zeros(Nx,Ny,Nz);
counter=0;

for i=nitstart:nitend
tfilename=(['T.' iterations((i),1:10) ]) ;
t=rdmds(tfilename,'b');
ufilename=(['U.' iterations((i),1:10) ]) ;
u=rdmds(ufilename,'b');
vfilename=(['V.' iterations((i),1:10) ]) ;
v=rdmds(vfilename,'b');
sumtheta=sumtheta+t;
sumu=sumu+u;
sumv=sumv+v;
counter=counter+1;
end
meantheta=sumtheta/counter;
meanu=sumu/counter;
meanv=sumv/counter;


pv=zeros(Nx,Ny,Nz);
ff=zeros(Nx,Ny,Nz);
dx=dm;
dy=dm;

for j=1:Ny
ff(:,j,:)=f+(j-1)*dy*beta;
end

pv(1:Nx-1,1:Ny-1,1:Nz-1)=(meanv(2:Nx,1:Ny-1,1:Nz-1)/dx -meanv(1:Nx-1,1:Ny-1,1:Nz-1)/dx ...
                    -meanu(1:Nx-1,2:Ny,1:Nz-1)/dy +meanu(1:Nx-1,1:Ny-1,1:Nz-1)/dy ...
		    +ff(1:Nx-1,1:Ny-1,1:Nz-1)) ...
		    .*(meantheta(1:Nx-1,1:Ny-1,1:Nz-1)-meantheta(1:Nx-1,1:Ny-1,2:Nz))/dz;

t0=input('Enter temperature : ')

% Interpolate PV on T=T0 surface

h=zeros(Nx,Ny);
pvh=zeros(Nx,Ny);

meantheta(:,:,Nz)=0.;
for i=1:Nx
for j=1:Ny
kk=find(meantheta(i,j,:)<t0);

if kk(1)>1
h(i,j)=(kk(1)-1)*dz+dz*(meantheta(i,j,kk(1)-1)-t0)/(meantheta(i,j,kk(1)-1)-meantheta(i,j,kk(1)));

pvh(i,j)=pv(i,j,kk(1)-1) ...
+(pv(i,j,kk(1))-pv(i,j,kk(1)-1)) ...
*(meantheta(i,j,kk(1)-1)-t0)/(meantheta(i,j,kk(1)-1)-meantheta(i,j,kk(1)));
else
h(i,j)=0;
pvh(i,j)=0;
end

end
end

hmax=max(max(h))


pcolor(pvh.');shading flat; colorbar; axis square
title(['mean PV from ' num2str(eval(itstart)) ' to 'num2str(eval(itend)) ' level of t=' num2str(t0) ]);
drawnow

figure

pcolor(squeeze(ff(:,:,2)).');shading flat; colorbar; axis square
drawnow

pcolor(h.');shading flat; colorbar; axis square
%pcolor(flipud(h.'));shading flat; colorbar; axis square
title(['mean H from ' num2str(eval(itstart)) ' to 'num2str(eval(itend)) ' level of t=' num2str(t0) ]);
drawnow

return