x or y intercept for 2D data

I have a 2D data of the form u(y, xi, l). Ie., 31x20x20, where 31 are values of y, 20 are u values that corresponds to 20 xi values and 20 corresponds to 20 l values. How can I find the y intercept of this data? Then plot the contour(xi, l, yintercept)

The code I added is for 1D data. The attached files are 2D data.

clc
uatL = load('u_L.mat');
%xi=load('xivals.mat');
%l= load("lvals.mat");
u_L = uatL.uxl;
y = load('y_vals.mat')

U=u_L(1,:); 
for k1 = 1:size(u_L,1)
    U = u_L(k1,:);
    Usign =sign(U);
    intsx = find(diff(Usign));            
    for k2 = 1:numel(intsx)
        idxrng = max(1,intsx(k2)-1) : min(numel(U),intsx(k2)+1);     
        yintercept(k1,k2) = interp1(U(idxrng), y(idxrng), 0);       
    end 
end

Unrecognized function or variable 'y'.

[Matt J]

As you can see from the output of your code above, y is missing. Also, please do us a favor and put all of your variables in a single .mat file, so that we don't have to download 4 separate files.

[Walter Roberson]

You do not use the xi or l that you load()

[University]

Sorry that I have to upload the files one by one. I have uploaded the y values one. The data u_L has computed for xi and l values already.

[University]

Hi Walter,

%

I want to a contour plot of y-location of intercept point of ( uxr and uxl) as a contour plot as a function of xivlas and Lvals.

I have tried the for one values of xivals and all lvals, which was successful. But I want the intercept for all xivals and all lvals.

for k1 = 1:size(uxl,1)

Ul = uxl(k1,:);

Usignl =sign(Ul);

intsxl = find(diff(Usignl));

for k2 = 1:numel(intsxl)

idxrngl = max(1,intsxl(k2)-1) : min(numel(Ul),intsxl(k2)+1);

yinterceptl(k1,k2) = interp1(Ul(idxrngl), y(idxrngl), 0);

end

end