reading values from a graph

I have written a code which gives me a graphical output called figure 2.

Now i want to make my code take the all the values from figure 2, at y = 0.5 and plot the graph and write the values in a new file.

Figure 2 can be found at,

http://imageshack.us/photo/my-images/208/figure2i.jpg/

The code i wrote to do that is,

for ly = 0.5

figure(4), plot (V)

fid = fopen('V1.txt','w');

fprintf(fid,' V = %5.3f \n',V)

status = fclose(fid);

end

But there is a problem with this code which i have written as this code is plotting and fprintf all the values from figure 2.

So anyone how can guide/help/show me how to improve my code so that it reads values at y = 0.5 from Figure 2 and plot a graph using those values.

Thank you & Warm Regards, Day

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This is the code which i use to create my figure 1 and figure 2.

if floor(25*k/nt)>floor(25*(k-1)/nt), fprintf('.'), end

   if k==1|floor(nsteps*k/nt)>floor(nsteps*(k-1)/nt)

% stream function

[Q,iter]=Stream(nx,ny,dx,dy,U,V);

   figure(1), contourf(x(1:nx),y(1:ny),Q(1:nx,1:ny)',20,'k-');colormap;

axis equal, axis([0 lx 0 ly]); title(sprintf('Re = %0.1g   t = %0.2g',Re,k*dt));

unode(1:nx,1:ny)=0.5*(U(1:nx,1:ny)+U(1:nx,2:ny+1));

vnode(1:nx,1:ny)=0.5*(V(1:nx,1:ny)+V(2:nx+1,1:ny));

figure(2), quiver(x,y,unode(1:nx,1:ny)',vnode(1:nx,1:ny)',2,'k-')

   hold on, axis equal, axis([0 lx 0 ly])

title(sprintf('Re = %0.1g   t = %0.2g',Re,k*dt))

   drawnow

end
end

[Jan]

What is the purpose of "for ly = 0.5"? Have you read the "help for" text already?

[iceuday]

I wrote for ly=0.5 because I was thinking by doing this I can get the code to plot V for the values at ly=0.5 from figure 2.

But the code does not do that. So how do I get the code to read values from figure 2 at ly=0.5 and plot those set of values?

[Fangjun Jiang]

Where is figure 2? What is V? I am not clear what you want do.

[iceuday]

figure 2 is a velocity field, i have uploaded the file but waiting for the file to be accepted and posted by file exchange.

V is the velocity in the y direction.

What i want to do is,

to obtain all the V velocity values from figure 2 at y=0.5 , so how am I going to write a code for that.

[Walter Roberson]

File exchange is not the right place for such things.

http://www.mathworks.com/matlabcentral/answers/7924-where-can-i-upload-images-and-files-for-use-on-matlab-answers

[iceuday]

Thank you Walter for the information.

Figure 2 can be found at this link below,

http://imageshack.us/photo/my-images/208/figure2i.jpg/

Figure 2 is a velocity field.

[Walter Roberson]

Your figure does not correspond to your plot command. When you use plot(V) then the x coordinates which would be implied would be x = 1 : length(V) but your figure is clearly labeled for x = 0 to 1.

Please show the actual plotting command that you use. Different plot mechanism have different ways that would be best for extracting the information you are interested in.

[iceuday]

I have included my code which creates my figure 1 and figure 2.

So how do i create my figure 4 using values at y = 0.5 from figure 2.

[Walter Roberson]

Insufficiently defined. Do you want the graphic all along the line y=0.5 (e.g., the locations where each if the quiver arrows cross y=0.5), or do you want the unode() and vnode() pairs that would correspond to y = 0.5 ?

Is y = 0.5 exactly in the list of y (as it looks like it might be), or will it be necessary to interpolate the surrounding fields in order to determine the data for y = 0.5 ?

If y = 0.5 is exactly in the list of y, then

yloc = find(abs(y - 0.5) < 100*eps(0.5), 1);

thisu = unode(:, yloc);

thisv = vnode(:, yloc);

That is, thisu and thisv would give the vector field values all along the line y = 0.5 .

That is, one would see, a pair of numbers for each x, but your sample code has the look of expecting V to be a vector, a single number per x. You will need to clarify what you are expecting.