Direction of Arrows in Quiver (2D)

this is related to the question asked here:

http://www.mathworks.com/matlabcentral/answers/48618-how-to-set-colors-in-quiver-2d

so I did make to seperate quivers for the inwards and outwards arrows. the new problem is, that some of my arrows that i think should be pointing outwards are pointing inwards.

as can be shown here: http://tinypic.com/view.php?pic=6zvdwk&s=6

here is how i created this, tell me where you think i am wrong:

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% find slope of profile

m_profile(2:45, :)=diff(z1)./diff(x1);

m_profile(1,:)=1.7612;

m_profile(29,:)=0;

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%find arrow slope according to m2=-1/m1

m_arrow=-1./m_profile; theta=atand(m_arrow);

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%create mark vector - indicating which arrows should point inweard(negative cp values)

for j=1:num

for i=1:45

    if cp_norm(j,i)<0

          mark(i,j)=1; %mark arrows pointing inwards

end end end

    % sort flagged control points - create 2 matrixes - one for inwards(flag) and one for outward (nflag) arrows
                k=1; l=1;
                flag=[];
                nflag=[];
                for i=1:45
                    if mark(i,j)==1
                        flag(k,1)=x1(i,j);
                        flag(k,2)=z1(i,j);
                        flag(k,3)=cp_norm(j,i)*cosd(theta(i,j));
                        flag(k,4)=cp_norm(j,i)*sind(theta(i,j));
                        k=k+1;
                    else
                        nflag(l,1)=x1(i,j);
                        nflag(l,2)=z1(i,j);
                        nflag(l,3)=cp_norm(j,i)*cosd(theta(i,j));
                        nflag(l,4)=cp_norm(j,i)*sind(theta(i,j));
                        l=l+1;
                    end
                end

still the result is some of the arrows are pointing inwards as you can see, where am i wrong?

thanks,

Noa

Answer 1

[José-Luis]

I'm gonna venture a wild guess. We don't know what your data looks like (well, except from the plot). However, this line:

m_profile(2:45, :)=diff(z1)./diff(x1);

would indicate that you are taking some sort of slope. However, you are only considering the forward difference. Maybe an average, the central difference, would give the results you want.