Problem with figures, plots behave oddly and are unusable

Hello,

I have been observing a problem related to all kinds of functions which plot something (plot, surf, contour etc). For example the following code results in a very distorted image

f=@(x) [x(1)^2-4*x(2)^2+3; x(1)-x(2)^2];

figure(1)

plotzeros(f, [-0.5 4], [-2.2 2.2])

Ihave tried to uninstall and reinstall MATLAB, however nothing has changed. What should I do to solve the problem?

Thank you.

[Dennis]

Can you provide a different example? I have never heard of a plotzeros function and have no clue what it might be doing.

Maybe also explain what you are trying to plot - you have 2 inputs and 2 outputs of your function. I would actually expect multiple lines from that (if you want a line plot).

[Valentina Sgarbossa]

I am sorry, I thought plotzeros was a built in function but I actually got it from my professor.

The function plots the zeros of bivariate functions, through the contour function.Here's the code:

function plotzeros(fun, x_limits, y_limits, varargin)

 plotzeros(fun, [X_MIN X_MAX], [Y_MIN Y_MAX], sample_len)
if nargin > 3
    sample_len = varargin{1};
else
    sample_len = 500;
end

v_dis_x = linspace(x_limits(1), x_limits(2), sample_len);
v_dis_y = linspace(y_limits(1), y_limits(2), sample_len);
n_dis_x = length(v_dis_x);
n_dis_y = length(v_dis_y);

Z_1 = zeros(n_dis_y, n_dis_x);
Z_2 = zeros(n_dis_y, n_dis_x);

for i = 1:n_dis_x
    for j = 1:n_dis_y
        
        funz = fun([v_dis_x(i); v_dis_y(j)]); 
        
        Z_1(j,i) = funz(1);
        Z_2(j,i) = funz(2);
        
    end
end

contour(v_dis_x, v_dis_y, Z_1, [0 0], 'Linecolor',[0 1 0], 'Linewidth', 2)
hold on
contour(v_dis_x, v_dis_y, Z_2, [0 0], 'Linecolor',[0 0 1], 'Linewidth', 2)
axis equal
set(gca, 'FontSize', 14)
grid on

end

Anyway, another example:

v1=([4 3]/5)'; v2=([-3 4]/5)';
l1=5; l2=10;
V = [v1,v2];
D1 = diag([l1,l2]);
A1 = V*D1*V';
l1=1; l2=10;
D2 = diag([l1,l2]);
A2 = V*D2*V';
b=[4 8]';
%so far we just created matrixes and vectors
x=linspace(-10,10,80); y=linspace(-10,10,80);
[X,Y]=meshgrid(x,y);
Phi1 = 0.5* ( A1(1,1)*X.^2 + A1(2,2)*Y.^2 + 2*A1(1,2)*X.*Y ) - b(1)*X - b(2)*Y;
Phi2 = 0.5* ( A2(1,1)*X.^2 + A2(2,2)*Y.^2 + 2*A2(1,2)*X.*Y ) - b(1)*X - b(2)*Y;
surf(X,Y,Phi1,'Lines','no'); title('phi 1'); hold on
contour(X,Y,Phi1,20)

And this is the resulting plot

[darova]

Look HERE

Maybe it has something to do with this

[Valentina Sgarbossa]

Thank you very much!

Indeed the problem was with the driver of the graphic card, so the command

opengl software 

put figures back to normal.

[Jan]

Thanks Valentina! I really love the image in the question. It is one of the best Matlab diagrams I've ever seen! :-)

[Adam Danz]

It looks like it was made with the Jackson Pollock toolbox.