Quiver plots using data from a loop

I hope someone can help me with the following quiver mysterious.

I would like to plot velocity vectors as arrows with components (u,v) at the points (x,y). However, from the whole set of data, I would like to display only every certain x values (vertical lines) as in figure 1. I use a loop to obtain only the data that I would like to plot (i.e. every 140 values). Since I would like to use these specific data as matrix, I create X,Y,U,V. When I plot quiver of X,Y,U,V the plots are different. In particular,it seems one line starts differently than the next one (beginning of the grid columns)

I have tried using structures and I get the same. I check the matrix X,Y,U and V and they are the sames than by using the loop. Therefore I cannot understand why I dont get the same plot.

Could anyone explain me the reason?

Thanks

Thanks a lot in advance

------------------------------------ m1=1;

 for k=1:140:length(x(1,:))  

    xp=x(:,k);
    yp=y(:,k);
    up=u(:,k);    
    vp=v(:,k);

    X(:,m1)=xp;
    Y(:,m1)=yp;
    U(:,m1)=up;
    V(:,m1)=vp;

figure(1) 

       h3=quiver(xp(1:15:end),yp(1:15:end),up(1:15:end),vp(1:15:end),1);

      hold on

        axis([0 600 0 70])

m1=m1+1;

end

figure(2)

     h4=quiver(X(1:15:end),Y(1:15:end), U(1:15:end),V(1:15:end),1);
     axis([0 600 0 70])

Figure 1:

Figure 2:

[Sean de Wolski]

I'm not clear on what you want and don't want.

[600Seat]

u,v data means velocity field of a flow. The x values mean distance in horizontal, and the y values mean heights. I would like to plot the field velocity only every certain distance in x. Lest say I would like to get all u,v for x= 0, 55, 110, etc. As it is plot in figure 1. In order to get the figure 1, I created a loop where I only read data every certain increment and the plot is created line by line according to the for end command, as following:

 for k=1:140:length(x(1,:))  

    xp=x(:,k);
    yp=y(:,k);
    up=u(:,k);    
    vp=v(:,k);
igure(1) 

       h3=quiver(xp(1:15:end),yp(1:15:end),up(1:15:end),vp(1:15:end),1);

      hold on

end

However, I dont want the plot to be created line by line as part of the loop. I would like to keep the 'important' data in a matrix with x,y,u,v values and to plot it outside the loop. For this, I created a counter m=1, m=m+1 and matrix to keep the values, i.e. X(:,m1)=xp; Y(:,m1)=yp; U(:,m1)=up; V(:,m1)=vp;

However, when I plot the values of X,Y,U and V after the loop ends (figure 2) the velocity values are not exactly the same. In particular, if you look at the grid (because there is a lot of zeros for u and v), figure 1 is squared but figure 2 is more like diagonal...

Why figure 1 is different than figure 2?

I hope it is a little more clear now.

thanks a lot in advance