% This m file plots a plane and a cone in 3-Space

x = -2 : 0.05 : 2; % x as a vector
y = transpose(x); % y as a vector
[X, Y] = meshgrid(x, y); % x and y as matricies
%Zplane1 = 1 + X;
%Zplane2 = 1 - 3 * X;
%Zcone = (X .^ 2 + Y.^2) .^ (1/2);

for i = 1 : length(x)
  for j = 1 : length(x)
    point = 1 + x(i);
    if ((point <= 2) & (point >= 0))
      Zplane1(i, j) = point;
    else
      Zplane1(i, j) = NaN;
    end
    point = 1 - 3 * x(i);
    if ((point <= 2) & (point >= 0))
      Zplane2(i, j) = point;
    else
      Zplane2(i, j) = NaN;
    end
    point = (x(i) ^ 2 + y(j)^2) ^ (1/2);
    if ((point <= 2) & (point >= 0))
      Zcone(i, j) = point;
    else
      Zcone(i, j) = NaN;
    end
  end
end



surf(X, Y, Zcone);
figure;
surf( X, Y, Zplane1);
figure;
surf( X, Y, Zplane2);