如何绘制Octave \\ Matlab函数输出？

Question

I everyone, I am pretty new in Octave\\MatLab and I have the following doubt. I have this code calculating a sigmoid function for a parameter z:

function g = sigmoid(z)
%SIGMOID Compute sigmoid function
%   g = SIGMOID(z) computes the sigmoid of z.

% You need to return the following variables correctly 
g = zeros(size(z));

% ====================== YOUR CODE HERE ======================
% Instructions: Compute the sigmoid of each value of z (z can be a matrix,
%               vector or scalar).

g = 1 ./ (1 + exp(-z));

% =============================================================

end

z could be a scalar, a vector or a matrix.

For example doing something like this:

>> X = [1 2; 0 5]
X =

   1   2
   0   5

>> g = 1 ./ (1 + exp(-X));
>> g
g =

   0.73106   0.88080
   0.50000   0.99331

Given the matrix X having 2 features X1 and X2 (the 2 column) how can I plot this function? The output is a three dimensional function?

Answer 1

The output is not a 3D function because you have one input X , and one output g , it's 2D.

You can display it column by column , displaying each column as a separate function on the same plot:

plot(X, g)

which is equivalent to:

figure
hold on
for i = 1:size(X,2)
    plot(X(:,i), g(:,i))
end
hold off

You can display it row by row , displaying each row as a separate function on the same plot:

plot(X', g')

which is equivalent to:

figure
hold on
for i = 1:size(X,1)
    plot(X(i,:), g(i,:))
end
hold off

You can display it as an array :

plot(X(:), g(:))